BEIRUT  - Islamic State group militant battling for control of the Syrian town of Kobane have suffered some of their heaviest losses yet in 24 hours of clashes and US-led air strikes.

At least 50 militant were killed in the embattled border town in suicide bombings, clashes with Kobane's Kurdish defenders and the air strikes, the Syrian Observatory for Human Rights said on Sunday.

The Britain-based monitor also reported that the US-led coalition battling the IS group hit at least 30 targets in and around Raqa, the militant' de facto capital.

There were no immediate details of a toll in the Raqa strikes, which the Observatory called one of the larger waves of raids by the coalition since it began its campaign in Syria in September.

In southern Daraa province, regime strikes killed at least 19 civilians, among them seven women and two children.

The deaths in Kobane came on Saturday after IS militant launched an unprecedented attack against the border crossing separating the Syrian Kurdish town from Turkey. Kurdish officials and the Observatory alleged the attack was launched from Turkish soil, a claim dismissed by the Turkish army as "lies".

IS began advancing on Kobane on September 16, hoping to quickly seize the small border town and secure its grip on a large stretch of the Syrian-Turkish border, following advances it made in Iraq.

At one point it looked set to overrun the town, but Kurdish Syrian fighters, backed by coalition air strikes and an influx of Iraqi Kurdish peshmerga forces, have held back the group.

In Raqa province, the coalition carried out strikes against at least 30 IS targets on the northern outskirts of Raqa city and struck Division 17, a Syrian army base militant captured earlier this year.

Observatory director Rami Abdel Rahman said the strikes had caused casualties, but there was no immediate toll available. "We can't say it's the largest set of raids they have carried out, but it's been a long time since we've seen this number of targets hit," he said.

The coalition began carrying out air strikes against the Islamic State group on September 23, and stepped up raids in Kobane in a bid to prevent it falling to IS.

On Thursday, the coordinator of the coalition said at least 600 IS fighters had been killed in air strikes and that the group had made easy targets of its fighters by pouring them into Kobane.

"ISIL has in so many ways impaled itself on Kobane," said retired US general John Allen, using a variant of the name for IS.

But Syria's Foreign Minister Walid Muallem, speaking from Russia after meeting key regime ally President Vladimir Putin, said the air strikes were having little effect.

"Is Daesh weaker today after two months of coalition strikes? All the indicators show that it is not," he told the pan-Arab Al-Mayadeen news channel.

He said unless Turkey closed its border to militant, the group would be unharmed by the air strikes.

Damascus has regularly accused Turkey of supporting "terrorism" because of its support for the Syrian opposition.

Turkey denies the allegations, but has made no secret of its backing for the opposition, with President Recep Tayyip Erdogan calling for Syria's President Bashar al-Assad to step down.

Despite their differences, Erdogan is set to receive Putin in Ankara on Monday for talks about the conflict, which began in March 2011 and has killed nearly 200,000 people.

The regime has kept up its deadly strikes, including raids that killed 19 civilians including seven women and two children in Jassem in southern Daraa province on Sunday.

Turkey also hosted Pope Francis this week, who used his visit to urge protection of the Middle East's Christian population against threats by militant.

"The terrible situation of Christians and all those who are suffering in the Middle East calls not only for our constant prayer, but also for an appropriate response on the part of the international community," the Pope said in a joint statement with Orthodox Ecumenical Patriarch Bartholomew I.

Meanwhile, a Syrian woman and her three sons were killed overnight in the government-held side of Aleppo city by rebel fire, the Syrian Observatory for Human Rights said.

The woman and her children were killed when a homemade rocket fired from the rebel-held east of the city hit their home around midnight in the Ashrafiyeh district, the Observatory said.

The Britain-based monitor said rebels were firing homemade explosive devices often using gas canisters that were even more damaging than regular mortar fire.

Aleppo, Syria's second city and former industrial powerhouse, has been divided between rebel control in the east and regime control in the west since shortly after fighting began there in mid-2012.

Since the end of 2013, the Syrian air force has regularly dropped explosive-packed "barrel bombs," which rights groups criticise as particularly indiscriminate, on the rebel east and surrounding province.

The barrel bomb attacks have killed several thousand people in Aleppo province, according to the Observatory.