BEIRUT - Syrian government warplanes bombed Kurdish-held areas of the northeastern city of Hasaka on Thursday for the first time in the five-year-old civil war, the Syrian Kurdish YPG militia and a monitoring group said.

People’s Protection Units (YPG) spokesman Redur Xelil said the air strikes had hit Kurdish districts of the city, which is mostly controlled by Kurdish groups, and the positions of a Kurdish security force known as the Asayish. “There are martyrs and wounded,” he told Reuters. The Syrian military could not immediately be reached for comment.

The YPG controls wide areas of northeastern Syria, where Kurdish groups have established an autonomous government, exploiting the unravelling of central state authority over the country since the start of the conflict. The Syrian government still has footholds in the cities of Qamishli and Hasaka, both in Hasaka governorate, co-existing largely peacefully with YPG-held swathes of territory. The cause of this week’s flare-up was unclear.

Tensions erupted between pro-government forces and Kurdish groups in Hasaka on Tuesday, leading to the most significant violence between the sides since several days of fighting in Qamishli in April.

Xelil said government forces were bombarding Kurdish districts of Hasaka with artillery, and there were fierce clashes in the city.

The Syrian Observatory for Human Rights, which tracks the war using a network of activists, said warplanes had targeted Kurdish security forces’ positions in the northwest and northeast of the Hasaka city.

The Observatory also said clashes were taking place in a number of positions around Hasaka.

Syria’s complex, multi-sided war has created a patchwork of areas of control across the country, with parts controlled by the government, rebels, Kurdish forces and Islamic State.

The YPG makes up a significant portion of the US-backed Syria Democratic Forces (SDF), a Kurdish and Arab alliance that fights against Islamic State insurgents in Syria. Last week the SDF, backed by air strikes from the US-led anti-IS coalition, said they had ousted Islamic State from the city of Manbij near the Turkish border after a two-month campaign.

Meanwhile, Russia said on Thursday it was ready to halt fire for 48-hour periods in Aleppo from next week, following UN calls to extend humanitarian pauses to deliver aid.

“Russia’s defence ministry is ready to support the proposal by UN envoy to Syria Staffan de Mistura regarding the introduction of weekly 48-hour ‘humanitarian pauses’ (in Aleppo),” defence ministry spokesman Igor Konashenkov said in a statement.

“We are ready to implement the first 48-hour ‘humanitarian pause’ to deliver humanitarian aid to Aleppo residents as a ‘pilot project’ already next week in order to ensure safe cargo deliveries to the city’s civilians.”

“Specific dates and times will be determined after information regarding the readiness of humanitarian convoys is received from the UN, as well as confirmation of safety guarantees from American partners,” he said. Russia last week declared it would hold three-hour pause in artillery fire and airstrikes daily around the ravaged Syrian city but the UN decried this as insufficient to help the approximately 1.5 million people in Aleppo.

Mistura insisted on a 48-hour halt, saying the logistics along mined and destroyed roads made access impossible in just three hours and endangered aid workers. The EU on Thursday called for an “immediate halt” to fighting, as the UN said aid was not reaching the besieged residents desperate for food and care.

Russia has flied an air strike campaign in Syria since September to help troops loyal to long-time Moscow ally Bashar al-Assad fight rebels and Islamist militants in the country.

Syrian and Russian aircraft have launched intense air strikes on opposition strongholds in northern Syria to prevent rebels sending reinforcements to a crucial battle in Aleppo, a monitor said Thursday.

Air strikes on Idlib city, 60 kilometres (35 miles) southwest of Aleppo, killed 25 people including 15 civilians on Wednesday, according to the Britain-based Syrian Observatory for Human Rights.

Regime aircraft continued to pound rebel positions across Idlib province on Thursday as well as parts of Aleppo province, it said.

“Regime and Russian aircraft are carrying out dozens of raids every day on Idlib province and the west of Aleppo province to prevent reinforcements reaching rebel positions,” said Observatory head Rami Abdel Rahman.

Idlib is dominated by the same alliance of rebels and militants that is fighting in Aleppo, including the former Al-Nusra Front, which has renamed itself Fateh al-Sham Front after renouncing its status as Al-Qaeda’s Syrian affiliate.

Southern Aleppo has been the scene of intense fighting since July 31, when the “Army of Conquest” alliance launched a major offensive to break a regime siege of opposition-controlled districts in the city’s east.

It took the southern district of Ramussa on August 6, linking up with opposition-held neighbourhoods. But neither side has achieved a decisive victory despite hundreds dead on both sides. Each side is now trying to cut off the other’s supply routes.

Despite its air power, the regime has been unable to gain headway in street-to-street battles, said Abdel Rahman. “The rebels have put all their forces into this battle and regime forces have been exhausted,” said Abdel Rahman.

Aleppo has been roughly split between opposition control in the east and government forces in the west since mid-2012.

Analysts say a decisive breakthrough by one side in Aleppo is unlikely for the time being.

On Thursday, the regime continued to pound the east of Aleppo city, where 146 civilians including 22 children have died in air strikes since 31 July.

More than 290,000 people have been killed and millions displaced since the beginning of Syria’s civil war, which started in 2011 with anti-regime protests.