Islamic State jihadists pushed into the key Syrian town of Kobane on the Turkish border Monday, seizing three districts in the city's east after fierce street fighting with its Kurdish defenders.

Kobane, also known as Ain al-Arab, has become a strategic battleground between the IS group and its opponents, who include the United States and its Western and Arab allies.

Taking Kobane would give the IS organisation control of a long stretch of the Syria-Turkey border.

The jihadists launched their latest assault on Kobane after a three-week siege with a wave of suicide bomb attacks, Mustefa Ebdi, a Kurdish activist from the town, said on his Facebook page.

After penetrating the city, they waged street battles against Kurdish defenders, sending hundreds of civilians fleeing towards the Turkish border, the Syrian Observatory for Human Rights said.

"They have taken the industrial zone, Maqtala al-Jadida and Kani Arabane in eastern Kobane after violent combat with Kurdish People's Protection Units (YPG) fighters" who had far fewer men and arms, said the Observatory.

Kurdish fighters meanwhile ordered all civilians to evacuate Kobane, Mustafa Bali, a spokesman for Kurds in the city, told AFP, adding that some 2,000 people had left the city.

The IS advances came after an AFP photographer saw two black flags of the jihadist group flying on Kobane's eastern side.

In a sign of mounting desperation, a Kurdish female fighter blew herself up at an IS position east of Kobane on Sunday, the Observatory said.

It was the first reported instance of a female Kurdish fighter employing a tactic often used by the jihadists, said the Britain-based monitor, which relies on a network of sources inside war-ravaged Syria for its reports.

- Suicide bombers -

The bomber, in her 20s, was a full-time YPG fighter identified as Dilar Gencxemis, alias Arin Mirkan, from Kurdish-controlled Afrin in northwestern Syria.

"She killed dozens of gang members and demonstrated the YPG fighters' determined resistance," her group said.

On another front, twin IS suicide truck bombings killed at least 30 YPG fighters and security officers on Monday in the Kurdish town of Hasakeh, northeast Syria, the Observatory said.

The jihadists had sparked further outrage at the weekend with the release of a video showing the beheading of Briton Alan Henning.

The video -- the latest in a series of on-camera beheadings of Western hostages -- also included a threat to another hostage, US aid worker Peter Kassig.

His parents have issued a video plea for their son's release, urging his captors to show mercy towards the 26-year-old former US soldier who has converted to Islam.

They also revealed Kassig had sent them a letter in June.

"I am obviously pretty scared to die but the hardest part is not knowing, wondering, hoping and wondering if I should even hope at all," Kassig wrote.

- 'NATO to protect Turkey' -

IS began advancing on Kobane on September 16, seeking to cement its grip over a long stretch of the border. The offensive prompted a mass exodus, with some 186,000 people fleeing into Turkey.

The Turkish security forces used tear gas Monday to push dozens of reporters and Kurdish civilians away from the border zone, which has become increasingly dangerous because of stray mortar fire.

Parliament in Ankara last week authorised the government to join a US-led campaign against IS, but so far no plans for military action have been announced.

The new head of NATO on Monday vowed to protect member Turkey against any IS attack.

"Turkey is a NATO ally and our main responsibility is to protect the integrity, the borders of Turkey," said NATO chief Jens Stoltenberg.

British media, meanwhile, reported that Turkish hostages freed by IS last month may have been released as part of a prisoner exchange for up to 180 jihadist fighters.

The Times newspaper cited a list it had received saying that among them were three French nationals, two British, two Swedes, two Macedonians, one Swiss and one Belgian.

Extremist Sunni Muslim group IS has seized large parts of Syria and Iraq, where it has been accused of carrying out widespread atrocities, including mass executions, abductions, torture and forcing women into slavery.

After first launching strikes against IS in Iraq in August, Washington has built a coalition of allies to wage an air campaign against the group.

In Syria, the coalition carried out anti-IS strikes on Sunday and Monday near Raqa, Deir Ezzor and Kobane, where two jihadist "fighting positions" were destroyed, said US Central Command.

In Iraq, they also launched three raids, targeting the jihadists near Fallujah and Ramadi, it said, adding Belgium and Britain took part in the strikes.

On Monday, officials said the US military has started flying attack helicopters against the jihadists in Iraq for the first time, marking an escalation in the air war that puts American troops at higher risk.

In all, nearly 2,000 air raids had been launched by the coalition in both Iraq and Syria, US defence officials said.

Some 1,768 air strikes were carried out by US warplanes while other coalition aircraft were responsible for 195 others, or about 10 percent of the total.

Ex-French agent is Syria jihadist, report says as Paris denies
Paris (AFP) Oct 06, 2014 - A former French intelligence officer who defected to Al-Qaeda was targeted by US air strikes in Syria last month, US media reported Monday, in an account promptly denied by Paris.

The alleged defector was associated with Al-Qaeda militants in Syria suspected of plotting to smuggle non-metallic bombs aboard passenger aircraft bound for Western countries, ABC television reported, citing two unnamed intelligence officials.

The targeting of the defector was first reported by the McClatchy news service.

According to the reports, European intelligence sources describe the former agent -- who allegedly defected from either French military intelligence services or the country's foreign spy agency the DGSE -- as the "highest ranking defector ever to go over to the terrorist group."

The French national, who reportedly joined Al-Qaeda in Afghanistan and went to Syria, was one of the targets of a round of US air raids in Syria aimed at the Al-Nusra Front, Al-Qaeda's Syrian affiliate, McClatchy wrote. US officials at the time said the air strikes were aimed at the "Khorasan" group, describing it as a collection of Al-Qaeda veterans.

The United States has launched a bombing campaign in Syria and Iraq as part of a coalition fighting jihadists in both countries -- mainly those belonging to the radical Islamic State group that controls large swathes of territory.

France's defence ministry denied any of its former agents was involved. "The report that the person allegedly belonged to the defence ministry's intelligence services is completely and utterly wrong," a ministry official told AFP.

The DGSE, meanwhile, refused to comment, as did France's foreign ministry.

According to the McClatchy report, the alleged former officer is an expert in explosives and is still alive despite the air strikes.

In Washington, the Central Intelligence Agency and the US military declined to comment.