The Lebanese army has gone on alert along the border with Syria and inside Lebanese territories after Russian jets intensified their airstrikes in central Syria and Hizbullah got more involved in the country's war.

A security source told As Safir daily published on Tuesday that terrorist groups taking refuge in the border area are making suspicious moves.

Hizbullah buried a leading commander in the south of the country on Monday, after he was killed "performing his jihadist duties in Syria", his party said.

"The Islamic Resistance (armed wing) is celebrating a leader from its heroic, sacrificing forces, the martyr Hassan Hussein al-Hajj... who died while performing his jihadist duties in Syria," it said in an official obituary.

Russia's security services said on Monday it foiled a "terrorist attack" on Moscow's public transport system by a group of militants, some of whom were trained by Islamic State jihadists in Syria.

A statement by the federal security service (FSB) said they had detained a group of people in Moscow and seized bomb-making materials they were planning to use in an attack on the capital's busy transport system.

Syrian regime forces backed by Russian air strikes advanced in the center of the country on Monday, sparking the fiercest clashes with rebels since Moscow began its air campaign, a monitor said.

The Syrian Observatory for Human Rights said regime forces had entered the village of Kafr Nabuda in Hama province as they press an operation on both sides of the highway between the capital Damascus and second city Aleppo.

Britain must accept more Syrian refugees faster in response to a humanitarian crisis of people fleeing conflict, a group of over 300 lawyers demanded in a statement released Monday.

The group, which includes a former president of Britain's supreme court and other prominent figures, called for the suspension of a system whereby asylum seekers claim asylum in the first EU country to which they arrive.

France's defense ministry said Monday it could not confirm whether French jihadists had been killed in air strikes on a training camp for Islamic State militants in Syria.

A source in the delegation of Prime Minister Manuel Valls, currently visiting Jordan, earlier said the strikes hausd probably killed French jihadists.

A Syrian priest who was kidnapped in May in the central province of Homs is free and on Sunday conducted his first mass since his abduction, a church source said.

"Father (Jacques) Mourad is free. He is currently in the village of Zaydal," about five kilometers (three miles) from the city of Homs, the source told AFP.

Syrian government troops backed by Russian air strikes advanced against rebels Sunday, as a rights group accused Moscow of being behind a new type of cluster bomb in the conflict.

Twelve days into Russia's aerial campaign, the troops were gaining ground on two fronts: in central Hama province around the Damascus-Aleppo highway, and in the northern part of regime stronghold Latakia province.

Rebels battled Saturday to reverse an Islamic State group advance on Syria's Aleppo, as Washington said it would resume talks with Moscow to avoid accidents in the skies over the war-torn country.

Moscow meanwhile continued its aerial campaign in Syria, launching a series of new strikes overnight and into Saturday targeting areas in and around the regime stronghold of Latakia province.

Iran on Friday declined to confirm a claim by a U.S. official that Russian missiles targeting rebels in Syria crashed in its territory this week.

"We don't confirm" this information, foreign ministry spokeswoman Afkham Marzieh said when asked about the claim.