Iraqi Kurdish peshmerga fighters have crossed into Syria from Turkey to help defend the embattled town of Kobani from Islamic State militants.

Around 150 fighters cheered and brandished rifles as they made the short trip across the border. They were applauded by fellow Kurds who lined the road leading to Syria.

The fighters will join Syrian Kurds in Kobani who - backed by US-led airstrikes - have been engaged in fierce clashes against IS.

Turkey finally gave in to US pressure to allow the Iraqi Kurdish forces to join the battle last week.

Ankara's decision was condemned by Damascus, which called it a "flagrant violation of Syrian sovereignty".

The battle for Kobani, which has been under siege for six weeks, has left an estimated 800 people dead and forced over 200,000 people to flee into Turkey.

Further fighting was reported by the Britain-based Syrian Observatory for Human Rights on Friday, which said coalition airstrikes had destroyed IS artillery pieces and left a number of militants dead.

"Kurdish fighters were able to advance towards an IS position in the north of the town after an operation that killed dozens of jihadists," it said.

Britain has so far limited its involvement in the US-led operation against IS to airstrikes in Iraq.

The Foreign Office (FCO) has warned that in light of the UK's contribution, Britons abroad could be targeted by possible revenge attacks.

It updated its travel advice to reflect a "heightened threat" of attacks across the globe from "groups or individuals motivated by the conflict in Iraq and Syria".

The FCO urged all Britons living or travelling overseas to remain "vigilant," but specified that the move was not a response to a specific threat.