Al-Nusra Front threatened Monday to use force to “liberate” its prisoners in Lebanon's jails, warning that the fate of the captive Lebanese security personnel would be at stake should Hizbullah wage an attack on the Syrian Qalamun region.

Meanwhile, Interior Minister Nouhad al-Mashnouq described Nusra's threat to kill the troops as “not serious,” telling a delegation from their families that their liberation is “a duty, a commitment and a national responsibility that has no room for leniency or procrastination and that won't be subject to bargaining."

The German government said it did not pay to secure the release earlier this year of a 27-year-old German national kidnapped in Syria by jihadist militants.

The U.N. Monday accused jihadists in Iraq of waging a campaign of "ethnic and religious cleansing", as Syria said it was ready to work with the global community against "terrorism".

The accusation by U.N. human rights chief Navi Pillay came as Kurdish peshmerga forces pushed back Islamic State (IS) jihadists northeast of Baghdad a day after the militants overran a key military airport in Syria.

Kurdish peshmerga forces supported by Iraqi air strikes pushed back jihadist fighters in northern Iraq on Monday, even as the militants overran a key military airport in neighbouring Syria.

A group of gunmen deployed on Monday in the northeastern border town of Arsal, media reports said, a day after militants raided the houses of residents, who are staunch supporters of the Lebanese army.

“More than 100 Lebanese and Syrian armed men in civilian clothes are deploying in Arsal,” Voice of Lebanon radio (93.3) reported.

Interior Minister Nouhad al-Mashnouq stressed on Monday the importance of “secrecy” regarding the case of the security personnel, who were taken hostage by Islamist gunmen in the northeastern border town of Arsal.

“Efforts are ongoing on all levels to ensure the safe release of the abductees,” Mashnouq said in comments published in As Safir and An Nahar newspapers.

A young American who has been held hostage for two years by an Islamic rebel group in Syria was released Sunday to U.N. peacekeepers in the Golan Heights, U.S. and U.N. officials said.

"Finally he is returning home," U.S. Secretary of State John Kerry said in a statement, confirming the release of Theo Curtis, an American researcher whose disappearance in Syria had not been previously reported.

The family of murdered U.S. journalist James Foley offered prayers for the safety of is fellow hostages in Syria on Sunday as they prepared to take part in a memorial mass.

Foley's parents John and Diane Foley were joined by family-members, well-wishers and representatives of the world media for a mass in his home town of Rochester, New Hampshire.

British authorities are "close" to identifying the hooded Islamic State jihadist who beheaded American journalist James Foley, the British ambassador to the United States said Sunday.

"I can't say more than this but I know from my colleagues at home that we are close," said Ambassador Peter Westmacott.

Jihadists from the Islamic State group have seized Tabqa military airport, the last remaining Syrian army base in northern Raqa province, following a battle that left more than 500 combatants dead, a monitoring group and state media said Sunday.

"170 Syrian soldiers were killed on Sunday in the offensive which led to the IS jihadists seizing Tabqa airport," the Syrian Observatory for Human Rights said in an e-mail sent to Agence France-Presse.