ISTANBUL/BEIRUT - Turkey on Thursday called on Russia to carry out joint operations against Islamic State (IS) in Syria, after crucial talks between President Vladimir Putin and Turkish counterpart Recep Tayyip Erdogan aimed at ending a diplomatic crisis.

The comments by Foreign Minister Mevlut Cavusoglu came as a Turkish delegation was in Russia for talks aimed at coordinating actions on Syria and other bilateral issues.

"We will discuss all the details. We have always called on Russia to carry out anti-Daesh (IS) operations together," Cavusoglu said in a live interview with the private NTV television, adding that the proposal was still "on the table".

Cavusoglu urged Russia to fight against the "common enemy" of IS militants in Syria.

"Let us come together to concentrate our efforts on Daesh," he said using an Arabic name for the IS group. "Let's fight against the terrorist group together, so that we can clear it out as soon as possible," the minister said, warning that if unchecked the group continue to expand and spread into other countries.

Meanwhile, Russian air strikes on the Islamic State group bastion of Raqa in northern Syria on Thursday killed at least 30 people, including 24 civilians, a monitoring group said.

The Syrian Observatory for Human Rights said they were killed and dozens of people wounded when 10 Russian raids hit the city and its outskirts. The monitor said it had not yet confirmed how many of the remaining six people killed were civilians or IS militants.

The Britain-based Observatory - which relies on a network of sources inside Syria for its information - says it determines what planes carried out raids according to their type, location, flight patterns and the munitions involved.

Russia confirmed that six Tupolev warplanes carried out airstrikes around Raqa, but said it had demolished "a chemical weapons factory in the city's northwestern outskirts." The defence ministry said the raids also destroyed a weapons storage facility and a training camp for IS fighters to the north and southeast.

The ministry said that the militants had suffered "significant material damages" in the strikes and that "a large number of fighters have been killed."

The raids comes a day after the ministry said it would halt fire around Syria's ravaged city of Aleppo for three hours each day to allow humanitarian aid in, an initiative the United Nations said is insufficient to meet the city's needs.

The UN has called for urgent aid access to Aleppo and 48-hour weekly pauses for the aid deliveries, warning that civilians are at grave risk from water shortages and disease as fighting has intensified.

Fighting between government forces and rebels in Aleppo has intensified in the past month, with both sides sending in reinforcements.

The Russian security agency said Thursday it found weapons and explosives after raiding a string of locations in central Russia to shut down an online group spreading propaganda for Islamic State militants.

The FSB security service and the police "identified and thwarted" the activities of cells belonging to an international internet community "created for the propaganda of terrorist ideology and recruiting of fighters for the Islamic State", the FSB said in a statement.

The cells were based in Russia's central Sverdlovsk, Tyumen and Chelyabinsk regions, where the FSB said it conducted 27 searches Wednesday at the homes of alleged members, seizing computers and mobile phones containing militant propaganda material as well as pistols, hand grenades and explosives.

The FSB said that criminal cases have been opened against the alleged leader of one the cells and three members, whose online community uses the Tajik language, the state language of the Central Asian ex-Soviet republic of Tajikistan.

It also said the online community has more than 100,000 members spread throughout the former Soviet republics of Central Asia and the Middle East.

The FSB said in February it had detained seven alleged IS members in the Sverdlovsk region who were plotting to carry out terror attacks in major Russian cities, including Moscow and Saint Petersburg.

Both IS and Al-Qaeda's Syrian affiliate Al-Nusra Front have called for attacks in Russia in response to Moscow's bombing campaign in support of Syrian President Bashar al-Assad.

IS has already claimed a number of attacks on Russian soil, including a deadly shooting at an ancient citadel in Russia's volatile North Caucasus region of Dagestan last year.

Moscow has said part of the reason why it launched a bombing campaign in Syria last year was to prevent IS militants and other extremists from perpetrating attacks in Russia.

According to FSB figures released in December, nearly 2,900 Russians are fighting or have fought with the militants in Iraq and Syria.

Doctors in Syria's Aleppo made a heart-wrenching plea Thursday for the US to help civilians in the city, hit by fresh fighting despite a promised Russian aid window.

Even as Moscow pledged to pause strikes around the divided second city, it carried out raids further east on the Islamic State group bastion of Raqa that a monitor said killed 24 civilians.

A longtime ally of the regime in Damascus, Russia has provided air cover for pro-government forces for nearly a year, including in the escalating battle for Aleppo.

An estimated 1.5 million people still live in the battered city, including about 250,000 in rebel-held eastern districts.

Aleppo has been rocked by a recent surge in violence, with residents on both sides of the bloody front line living in fear of being trapped by renewed hostilities.

Doctors in the eastern half implored US President Barack Obama on Thursday to protect civilians from repeated atrocities in their city.

"Unless a permanent lifeline to Aleppo is opened it will be only a matter of time until we are again surrounded by regime troops, hunger takes hold and hospitals' supplies run completely dry," the letter said.

Moscow said it would hold fire around the city for three hours daily starting Thursday to allow access for desperately-needed aid.

The pause would see "all military hostilities, aviation strikes and artillery strikes" stop between 0700 GMT and 1000 GMT for an unspecified period.

Rebels and regime forces clashed in southern Aleppo throughout Thursday morning, said the Syrian Observatory for Human Rights.

"There were clashes all night and throughout the morning," said Observatory head Rami Abdel Rahman.

Rebels and allied militants broke through a three-week government siege of the city's eastern districts on Saturday, opening a new route for goods through the southern outskirts.

But an AFP correspondent in the eastern districts said trucks carrying food and other products were unable to enter the city Thursday because of intense bombardment.

Syrian state news agency SANA on Thursday said forces loyal to Damascus seized control of territory south of the city and "inflicted heavy losses" on the enemy. But it made no mention of the "humanitarian windows" announced by Russia.

Further east, Russian raids hit the IS stronghold of Raqa, killing at least 24 civilians and wounding 70 people, according to the Britain-based Observatory.

The monitor said another six people were also killed but it had not yet confirmed how many of them were civilians or IS militants.

The Russian defence ministry said the raids destroyed a "chemical weapons factory" on Raqa's outskirts as well as a weapons storage facility and IS training camp to the north and southeast.

The ministry's statement said the militants suffered "significant material damages" in the strikes and that "a large number of fighters have been killed."

Syria's conflict erupted in March 2011 and has since killed more than 290,000 people, forced millions to flee their homes, and has drawn in world powers on all sides of the war.

On Thursday, Turkey - which has backed rebel groups against President Bashar al-Assad - offered regime ally Russia the possibility of joint operations against IS in Syria.

The offer came one day after crucial talks between President Vladimir Putin and Turkish counterpart Recep Tayyip Erdogan aimed at ending a crisis in ties.

Signed by 15 of east Aleppo's 35 remaining doctors, the letter to Obama accuses Washington of inaction, saying it had seen "no effort on behalf of the United States to lift the siege or even use its influence to push the parties to protect civilians."

"We do not need tears or sympathy or even prayers, we need your action. Prove that you are the friend of Syrians," it said.

Dr Abu Al-Baraa, a paediatrician who signed the letter and spoke to AFP in the eastern districts, said he was forced to watch children "die in our arms" because of dwindling medical supplies and repeated bombardment.

"There were children that suffered from chronic diseases that need additional tests," he said. "Because of our limited capability, we were forced to just watch the child die."