MOSCOW (AFP) - The Kremlin on Thursday (Dec 3) said it welcomed British air strikes against Islamic State in Iraq and Syria (ISIS) militants in Syria but argued they lacked a legal basis and called for a broader coalition.

"We continue to welcome any action aimed at fighting terrorism, at fighting the Islamic State," Russian news agencies quoted Kremlin spokesman Dmitry Peskov as saying, referring to the group by its other name.

"We of course consider that if these actions are coordinated and if everybody acts as part of a single coalition, effectiveness can be significantly increased."

Britain joined the US-led bombing campaign over Syria on Thursday (Dec 3), hitting what its defence ministry said was an oil field held by ISIS jihadists just hours after a decisive parliamentary vote authorised air strikes.

Moscow has sought, so far without success, to get nations in the US-led coalition that oppose Syrian President Bashar al-Assad to work with its own forces flying a bombing campaign in Syria and Damascus in a broader coalition.

Peskov said Thursday (Dec 3) that Russia's "doors are open" for the creation of such a coalition that would include Moscow, the West and some Middle Eastern states.

Moscow, however, maintained that its bombing campaign in Syria - unlike that of the West - is legitimate because Assad had requested it to support Syrian troops' ground operations.

"From the point of view of international law, the only country that is acting legitimately (in Syria), is the Russian Federation," Peskov said.