MURSITPINAR, Turkey (AFP) - The Islamic State in Iraq and Syria (ISIS) group was taking heavy losses in the Syrian battleground of Kobane on Sunday as Iraqi forces fought the extremists buoyed by United States backing for top government security appointments.

US Secretary of State John Kerry said the appointment of defence and interior ministers after weeks of delay was a "very positive step forward" in the fightback against ISIS in Iraq, which Washington has made its priority.

But US-led warplanes launched 11 air strikes near Kobane on Saturday and Sunday, US Central Command said, helping the town's Kurdish defenders to repulse a new attempt to cut their supply lines into Turkey.

The Kurdish fighters, who have been under ISIS assault for more than a month, weathered fierce street fighting and at least two jihadist suicide bombings but the front line remained unchanged on Sunday, a Kurdish official said.

"(ISIS) brought in reinforcements... and attacked hard," Idris Nassen said by telephone."But thanks to air strikes and (the Kurdish fighters') response, they did not make any progress."

The ISIS fighters suffered heavy losses in Kobane, which has become a key prize as it is being fought under the gaze of the world's press massed just over the border in Turkey.

From Saturday into Sunday morning, a total of 31 militants died in the battle, said the Syrian Observatory for Human Rights.

Coalition air strikes near Kobane hit 20 ISIS fighting positions, five ISIS vehicles and two ISIS-held buildings, said Central Command, with the Observatory adding that they killed 15 jihadists.

Clashes on the ground killed another 16 jihadists and seven Kurdish fighters, said the Britain-based Observatory, which has a wide network of sources inside Syria.

A steady flow of bodies from the Kobane fighting have arrived at an IS-controlled hospital further east, the Observatory said.

The corpses of at least 70 jihadists had been brought into the mortuary in the town of Tal Abyad in the past four days.

The US military has said it sees "encouraging" signs in the battle for Kobane, although it warns the town may still fall.

On Sunday the White House said President Barack Obama called his Turkish counterpart Recep Tayyip Erdogan and that they pledged to "strengthen cooperation" against IS in Syria.

But US commanders have said repeatedly the main priority remains the battle against IS in neighbouring Iraq, where the jihadists swept through much of the Sunni Arab heartland north and west of Baghdad in June.

The minority community's grievances against the Shiite led-government were a major factor in the lightning advance and Washington has been piling pressure on Baghdad to form an inclusive government capable of mounting a fightback.

On Saturday, the remaining posts in a new government line-up were finally approved by parliament, including a Sunni as defence minister and a Shiite as interior minister.

"These were critical positions to be filled, in order to assist with the organising effort" against (ISIS), the US top diplomat said. "So we're very pleased."

With Washington voicing approval, Prime Minister Haidar al-Abadi's office announced that he is to head to Teheran on Monday to discuss the fightback with his other key ally.

Washington has acknowledged that Teheran has an important role to play in the battle against ISIS, although it has kept the main Shiite power out of the coalition it has forged against the extremists for fear of alienating Sunnis.

Abadi's talks in Iran are part of his bid "to unite the efforts of the region and the world to help Iraq in its war against the terrorist group", his office said.

Although it has not been part of the US-led coalition, Teheran has been a key backer of Abadi's government in its efforts to hold back the ISIS advance.

According to a senior Iraqi Kurdish official, it has deployed troops on the Iraqi side of the border in the Khanaqin area northeast of Baghdad.

Iranian forces also played a role in the Shiite Turkmen town of Amerli, where security forces and allied militiamen broke a months-long ISIS siege at the end of August, another senior Kurdish official has said.

Evidence also indicates that Iran sent Sukhoi Su-25 ground attack jets to Iraq, though it is unclear who subsequently piloted the aircraft.

As well as Syria, the US-led coalition is carrying out air strikes against ISIS in Iraq, including 10 on Saturday and Sunday. It has also deployed military advisers.