The US-led coalition has carried out fresh air strikes against jihadists in Syria and Iraq as Washington called for the battle against the Islamic State group to be taken to the Internet.

Fighting continued to rage for the strategic Syrian border town of Kobane, and in Iraq a car bomb explosion on Monday killed at least eight people in a Baghdad square after a suicide bombing reportedly left at least 14 pro-government fighters dead south of the capital.

An AFP reporter in Turkey just across the border from Kobane said fierce clashes were raging in the strategic Syrian town, where Kurdish fighters have been holding off an offensive by Islamic State fighters for weeks.

The US military said its warplanes carried out four more air strikes near Kobane on Sunday and Monday.

As the fighting intensifies, the Pentagon revised up its estimate of the cost of the air war, saying the price tag for the campaign was about $8.3 million a day.

But there was still no sign of promised reinforcements for Kobane's defenders, despite plans announced last week for Iraqi Kurdish peshmerga forces armed with heavy weapons to join them.

A senior Iraqi Kurdish official said the deployment was being held up by Turkey, which has agreed to allow the peshmerga to pass through its territory.

"We are ready to send them," said Mustafuz Qader, who heads the ministry responsible for the peshmerga.

Kobane has become a symbol in the battle against IS, an extremist Sunni group that has seized large parts of Syria and Iraq, declared an Islamic "caliphate" and committed widespread atrocities.

Washington has forged an alliance of Western and Arab nations to combat the group and on Monday met with coalition partners in Kuwait City to boost efforts to counter the jihadists' online propaganda.

- IS 'perverts the innocent' -

Retired US general John Allen, who is coordinating the US-led campaign against IS, said the group was promoting its "horrendous brand of warfare" online, where it "recruits and perverts the innocent".

"It is only when we contest ISIL's presence online, deny the legitimacy of the message it sends to vulnerable young people... it is only then that ISIL will truly be defeated," Allen said, using an alternative name for the group.

The coalition partners pledged to take steps to boost efforts to prevent the recruitment of foreign fighters for IS, including online.

Concern is growing over the group's online influence in attracting foreign fighters and promoting attacks by disaffected Muslims on Western targets.

The US military said the coalition had also carried out seven new strikes against IS in Iraq on Sunday and Monday, including near the key Mosul dam and southeast of the militant bastion of Fallujah.

Since air strikes began on August 8, the campaign -- which has involved about 6,600 sorties by US and allied aircraft -- has cost $580 million, said Pentagon spokesman Commander Bill Urban.

The Defense Department had previously put the average daily cost of the military operation at more than $7 million a day.

The higher figure reflected the increased pace of air strikes and related flights, a defence official told AFP.

But independent analysts say the Defense Department is underestimating the genuine cost of the war effort.

Some former budget officials and outside experts estimate the cost of the war has already exceeded a billion dollars, and that it could rise to several billion dollars in a year's time.

Washington has been seeking to build a broader international alliance in the fight against Islamic State militants.

Iraq has struggled to regain territory taken by IS in a lightning offensive in June, though it announced at the weekend that its forces had retaken the town of Jurf al-Sakhr south of Baghdad.

Sources said Monday a suicide bomber had subsequently detonated an explosives-rigged Humvee armoured vehicle near security forces and allied militiamen in the area, killing at least 14.

And a car bomb exploded in Baghdad's busy Wathiq Square on Monday night, killing at least eight people, officials said.

- Assault on Syrian city -

Syrian rebels were meanwhile reported to have launched a major assault on the government-held city of Idlib in a bid to consolidate their control over the country's northwest.

Fighters of Al-Qaeda affiliate Al-Nusra Front and Islamist rebel units attacked the city from all sides from dawn Monday, the Syrian Observatory for Human Rights said.

The rise of IS has destabilised the region, including in Syria's neighbour Lebanon where weekend clashes killed at least 16 people and forced thousands to flee a neighbourhood of second city Tripoli.

Lebanese soldiers quelled Islamist militants in their Tripoli stronghold of Bab al-Tebbaneh and were in full control Monday, earning praise for their courage from the United Sates.

"We condemn those who seek to sow chaos in Lebanon and are confident that the Lebanese people will persevere if they stand united in the face of this threat," State Department spokeswoman Jen Psaki said.

US air war on IS costing $8.3 million a day: Pentagon
Washington (AFP) Oct 27, 2014 - The Pentagon has revised its estimate of the cost of the US air war in Iraq and Syria, saying the price tag for the campaign against the Islamic State group comes to about $8.3 million a day.

Since air strikes began on August 8, the campaign -- which has involved about 6,600 sorties by US and allied aircraft -- has cost $580 million, said Pentagon spokesman Commander Bill Urban.

The Defense Department had previously put the average daily cost of the military operation at more than $7 million a day.

The higher figure reflected the increased pace of air strikes and related flights, a defense official, who spoke on condition of anonymity, told AFP.

But independent analysts say the Defense Department is underestimating the genuine cost of the war effort, which began in mid-June with the deployment of hundreds of US troops to secure the American embassy in Baghdad and to advise the Iraqi army.

Some former budget officials and outside experts estimate the cost of the war has already exceeded a billion dollars, and that it could rise to several billion dollars in a year's time.

Todd Harrison of the Center for Strategic and Budgetary Assessments projected the war could cost $2.4 to $3.8 billion a year, in an analysis issued on September 29.

If the intensity of the bombing raids is expanded, the air war could cost as much as $4.2 to $6.8 billion per year, according to Harrison's report.

One of the biggest drains on the budget for the air war are the large number of surveillance and reconnaissance flights that bombing raids require, analysts say.

The campaign, dubbed "Operation Inherent Resolve," has seen thousands of spy flights and aerial refueling runs.

The cost of flying the spy planes range from about $1,000 an hour for Predator and Reaper drones to $7,000 an hour for high-altitude Global Hawk drones, or as much as $22,000 per hour for E-8 J-STAR (Joint Surveillance Target Radar Attack System) aircraft.

Funds for the air war are coming out of the Pentagon's de facto war budget, the Overseas Contingency Operations fund.

Separate from the regular defense "base" budget, the OCO fund is often portrayed as a "credit card" to cover the costs of wars.

Congress increased the OCO budget to about $85 billion for last fiscal year, ending September 30. The proposed fund for the new fiscal year 2015 is due to drop to $54 billion.