Jihadists from the Islamic State group battling for control of the Syrian border town Kobane have suffered some of their heaviest losses yet in 24 hours of clashes and U.S.-led strikes.

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

Arsal prominent figure Sheikh Mustafa al-Hujeiri, who is also known as Abu Taqiyeh, denied on Sunday that he was tasked by the Lebanese state to negotiation the release of the abducted servicemen, warning of a “last chance” given by the jihadists to the government.

“The (al-Qaida-linked) Nusra Front has granted the government a last chance to engage in serious negotiations to release” the captive soldiers and policemen, Hujeiri told the pan-Arab daily Asharq al-Awsat.

The Lebanese state is reportedly waiting for the final names of the prisoners that the Islamic State group and al-Qaida-linked Nusra Front are demanding their release to exchange them with the captive soldiers and policemen.

According to al-Mustaqbal newspaper published on Sunday, the Lebanese state gave the green light to the prisoners swap deal, demanding the abductors to hand over to the Qatari-appointed negotiator Ahmed al-Khatib, the list of inmates they want their release.

U.S.-led strikes against the Islamic State group in Syria have failed to weaken the jihadist organization, according to Syria's Foreign Minister Walid Muallem.

Speaking on Friday night to two Middle Eastern television stations, Muallem also said "more time" was needed before a dialogue between the Syrian government and opposition could begin.

Islamic State group jihadists launched a double attack Saturday on a Kurdish-controlled post on the Syrian-Turkish border for the first time, prompting fierce clashes in the adjacent town of Kobane.

Kurdish officials and a Britain-based monitor said the two IS suicide attacks targeting the border post were launched from Turkish soil, claims that Turkish officials dismissed as "lies."

The Free Syrian Army urged Army Commander General Jean Qahwaji to release five of its members who were arrested in Lebanon earlier this month, reported As Safir newspaper on Saturday.

It said in a letter to Qahwaji: “The General Staff and the military council of the FSA reject the spike in arrests of members of the army.”

Conflicting reports emerged Friday evening on whether or not al-Nusra Front had backed down from its threat to execute captive soldier Ali al-Bazzal, as the General Security announced that the Qatari mediator will return to Lebanon “in the coming hours.”

“The General Security communicated with the Qatari side, which informed General Security chief Maj. Gen. Abbas Ibrahim that the Qatari mediator will return again to Lebanon in the coming hours,” state-run National News Agency reported.

Some 200 Syrian refugees protesting in Athens on Friday asked to be allowed access to other European countries, fearing deteriorating conditions in crisis-hit Greece.

"Crisis-hit Greece alone cannot support the weight of accommodating war refugees," said Nander Halbuni, a representative of the Syrians who have been camping on Syntagma Square in central Athens for over a week.

More than 500 people have been killed in 2,000 air strikes across Syria by regime forces over the past 40 days, a monitoring group said Friday.

The Syrian Observatory for Human Rights accused President Bashar Assad's government of "war crimes", saying it ought to be "listed in the Guinness Book of World Records" for the large number of strikes since October 20.

Prosecutors in the trial of an alleged German jihadist called Friday for him to be jailed for more than four years for having fought with the Islamic State group in Syria.

In the first German criminal proceedings involving IS, Kreshnik Berisha, a 20-year-old born near the business capital Frankfurt to a family from Kosovo, was charged with membership of a foreign terrorist organization.