The UK government has strongly rejected calls to cooperate with the Syrian regime to confront the Islamic State militant group.

Prominent politicians and former senior diplomats have argued that the Islamic State (also known as the Islamic State in Syria and the Levant — ISIL) could not be defeated without Syrian government cooperation.

Peter Hain, Labour MP and former Northern Ireland minister, and Sir William Patey, the former UK ambassador to both Iraq and Saudi Arabia, are among those who have advised that it would be impossible to defeat the Islamic State group unless the West talks to Syrian President Bashar Al-Assad.

However, David Cameron, the UK prime minister has ruled out the idea.

"I think President Assad is part of the problem, not part of the solution," he said.

In a television remark on the fringe of the NATO summit in Wales, Cameron reiterated that the Assad regime lost its legitimacy because of “his war crimes.”

The Syrian government earlier expressed its readiness to “cooperate and coordinate at the regional and international levels to fight terrorism within respect for the sovereignty and national soil of Syria.”

Cameron said Britain was offering support to the moderate Syrian opposition and the Iraqi government to help them in their battle against the Islamic State in both countries.

Meanwhile, Cameron did not rule out possible UK participation in air attacks on the Islamic State in Iraq.

Asked about his position if military assistance was requested by the Iraqi government, Cameron said air strikes would be legal.

"I certainly don't rule anything out. We should pursue our national interests,” he added.

The Islamic State currently has one British hostage in detention, who it has threatened to behead unless US air strikes on its positions in Iraq stop.

British aid worker David Haines was taken hostage in the village of Atmeh, in the Idlib province of Syria, in March 2013.

Despite initial UK support for US efforts to fight the Islamic State group, Cameron said no Western country can defeat the militant group alone.

He underlined that any action taken must not be "Western intervention over the heads of neighbouring states."

Saudi Arabia has already expressed support for an international coalition to defeat Islamic terrorism.

Iraq's president has announced his country will play a leading rule in this coalition, with the participation of Saudi Arabia and Iran.