French, US planes strike Islamic State; Britain to join coalition

French fighter jets struck Islamic State targets in Iraq on Thursday and the United States hit them in Syria, as a U.S.-led coalition to fight the militants gained momentum with an announcement that Britain would join.

The French strikes were a prompt answer to the beheading of a French tourist in Algeria by militants, who said the killing was punishment for Paris's decision last week to become the first European country to join the US led bombing campaign.

In the United States, FBI director James Comey said Washington had identified the masked Islamic State militant believed to have beheaded two American hostages in recent weeks, acts that helped galvanise Washington's bombing campaign.

Iraq's Prime Minister Haidar al-Abadi, in New York to attend a UN meeting, said on Thursday he had credible intelligence that Islamic State networks in Iraq were plotting to attack U.S. and French metro trains.

Senior US officials said they had no evidence of the specific threat cited by Abadi, but New York's governor said he and his counterpart in New Jersey were already beefing up transport security in light of possible Islamic State threats.

France had said earlier on Thursday it would boost security on transport and in public places after the killing of French tourist Herve Gourdel by Islamic State sympathisers in Algeria.

Britain, the closest US ally in the past decade's wars, finally announced on Thursday that it too would join air strikes against Islamic State targets in Iraq, after weeks of weighing its options. Prime Minister David Cameron recalled parliament, which is expected to give its approval on Friday.

While Arab countries have joined the coalition, Washington's traditional Western allies had been slow to answer the call from U.S. President Barack Obama. But since Monday, Australia, Belgium and the Netherlands have said they would send planes.

The Western allies have so far agreed to join air strikes only in Iraq, where the government has asked for help, and not in Syria, where strikes are being carried out without formal permission from President Bashar al-Assad. However, France said on Thursday it did not rule out extending strikes to Syria, too.

Overnight, US led air strikes in eastern Syria killed 14 Islamic State fighters, according to a monitoring group, while on the ground, Kurdish forces were reported to have pushed back an advance by the Islamists towards the border town of Kobani.

The air raids follow growing alarm in Western and Arab capitals after Islamic State, a Sunni militant group, swept through a swathe of Iraq in June, proclaimed a "caliphate" ruling over all Muslims, slaughtered prisoners and ordered Shi'ites and non-Muslims to convert or die.

"HARSHNESS, BRUTALITY, TORTURE AND MURDER"

More than 120 Islamic scholars from around the world, including many of the most senior figures in Sunni Islam, issued an open letter denouncing Islamic State. Challenging the group with theological arguments, they described its interpretation of the faith as "a great wrong and an offense to Islam, to Muslims and to the entire world".

"You have misinterpreted Islam into a religion of harshness, brutality, torture and murder," said the letter, signed by figures from across the Muslim world from Indonesia to Morocco.

A third night of air raids by the United States and Arab allies targeted Islamic State-controlled oil refineries in three remote locations in eastern Syria to try to cut off a major source of revenue for the al Qaeda offshoot.

The strikes also seem to be intended to hamper Islamic State's ability to operate across the Syria-Iraq frontier.

Obama has vowed to keep up military pressure against the group, which advanced through Kurdish areas of northern Iraq this week despite the air strikes. Some 140,000 refugees have fled to Turkey over the past week, many telling of villages burnt and captives beheaded.

"The only language understood by killers like this is the language of force, so the United States of America will work with a broad coalition to dismantle this network of death," Obama said at the UN General Assembly on Wednesday.

KURDS HALT ISLAMIC STATE ADVANCE

One danger the U.S.-led campaign has in Syria is the lack of strong allies on the ground. Washington remains hostile to the Assad government. It wants other Syrian opponents of Assad to step into the breach as Islamic State is pushed back, but such "moderate opposition" groups have had limited success.

One group that has fought hard against Islamic State on the ground in Syria are the Kurds, who control an area in the north but complain that they have been given no support from the West.

On Thursday, two Kurdish officials said Kurdish forces had pushed back the advance by Islamic State fighters towards the border town of Kobani in overnight clashes. Fighting near the town in recent days had prompted the fastest exodus of refugees of the entire three-year-old Syrian civil war.

Islamic State, which launched a fresh offensive to try to capture Kobani more than a week ago, concentrated its fighters south of the town for a push late on Wednesday, but Kurdish YPG forces repelled them, the Kurdish officials said.

"The YPG responded and pushed them back to about 10-15 km (6-9 miles) away," Idris Nassan, deputy minister for foreign affairs in the Kurdish administration in the area, told Reuters by telephone.

Ocalan Iso, a Kurdish defence official, confirmed that YPG forces had stemmed Islamic State's advances south of Kobani, known as Ayn al-Arab in Arabic.

"As our fighters secured the area, we found 12 Islamic State bodies," he said by telephone. Islamic State fighters also remain to the east and west of the town and fighting continues in the south.

Near Damascus, Assad's Syrian army overran rebels in a town on Thursday, strengthening the Syrian leader's grip on territory around the capital.

Assad's forces, backed by the Lebanese Shi'ite movement Hezbollah, have been gradually extending control over a corridor of territory from Damascus to the Mediterranean coast.

Many Syrian activists and rebels have criticised the United States for focusing on striking Islamic State and other militant groups while doing little to bring down Assad.