After more than two months of air strikes, a US-led coalition has prevented the fall of a northern Syrian town to Islamic State jihadists but is still struggling to halt the group's advances on other fronts, experts say.

Since the air war on the IS militants began on August 8, the United States and its allies have few concrete successes to point to as the IS group has continued to roll ahead in western Iraq and tighten its grip elsewhere.

But US officials insist it is too early to draw conclusions, and that a methodical effort will eventually bear fruit, as Iraqi and Kurdish forces build in strength.

"We're in the first couple of minutes of the ball game," said one senior officer at US Central Command, which oversees the air campaign.

Senior US administration officials and military commanders acknowledged in recent days the Iraqi army is months away from any sustained counter-offensive that could roll back the IS from its strongholds in Iraq's western and northern provinces.

And despite ambitious plans for Iraq's Sunni tribes to join the fight, most of the tribal leaders are sitting on the fence, waiting to see if the new Iraqi Prime Minister Haider Abadi will break with the sectarian politics of his predecessor, officials said.

In the Syrian border town of Kobane, US officials are cautiously optimistic that Kurdish fighters -- backed by US air raids -- have fended off a relentless push by the IS militants to seize control of the area.

By keeping the town from falling -- at least for the moment -- the Americans avoided handing the IS a potential propaganda coup in a battle that has drawn intense media attention.

But the fight remains a stalemate and the Kurds' desperate appeals for help -- and Turkey's cool response -- have highlighted the deep divisions that plague the anti-IS coalition, experts said.

-- Tenuous Coalition --

The US strategy's goals "cannot be realized because the interests of the different partners are diametrically opposed," said French General Vincent Desportes, professor of strategy at Sciences-PO in Paris.

The fragile coalition offers a contrast to the 1991 Gulf War, when the United States was able to forge common ground with Arab and European allies, he said.

"In 1991 something was achieved because the Americans succeeded in aligning with the Gulf States," he told AFP.

Turkey's role has been a constant source of tension. And the United States has underestimated Ankara's determination to avoid any action that would empower the Kurds, analysts say.

At the same time, Turkey and Arab governments are frustrated with Washington's reluctance to directly confront the Syrian regime.

European allies have treaded cautiously as well, signing up for air strikes in Iraq while abstaining from bombing the IS in Syria.

The goals of the war are still only vaguely defined and coalition members cannot agree on them, said a French official.

"There are a series of political problems that have repercussions for the military plan," said the official, who asked not to be named.

The initial objective of the war effort was to use air strikes to build a "firewall" that would stop the IS militants' progress, buying the coalition time to rebuild the Iraqi army and eventually launch counter-attacks.

- Ground gained, after strikes -

But after more than 630 air raids in Syria and Iraq, the IS has continued to gain ground -- particularly in western Anbar province -- and threaten other key fronts in the north.

The United States "has found that the Iraqi military forces are even weaker than it is original assessments indicated ...," according to Anthony Cordesman of the Center for Strategic and International Studies, a Washington think tank.

The scale of the air war has paled compared to the NATO intervention in Libya and some other campaigns, sparking accusations of a half-hearted effort.

Retired US Air Force commander David Deptula complained the air campaign is nothing more than a "drizzle" and that only a "thunderstorm" will suffice.

To strike a genuine blow at the IS group, analysts say President Barack Obama will have to ramp up the air raids and send US military advisers with local forces into combat, to ensure bombs hit their mark and that operations succeed.

US officers say the pace of the strikes has been limited in partly because commanders want to avoid civilian casualties and because Iraqi forces are not yet able to stage large-scale assaults.

They cite a successful operation in August when a mostly Kurdish force took back control of Mosul dam as an encouraging sign, proving local troops were capable of complicated missions.

Pentagon spokesman Rear Admiral John Kirby insisted there will be more successes like the one at Mosul dam: "What I can tell you is we believe the strategy is working; that the policy is sound, the coalition continues to gain both momentum and strength."

US-led aircraft pound IS group with 23 air strikes
Washington (AFP) Oct 25, 2014 - The US-led military coalition pounded the Islamic State group Friday and Saturday, with 22 air strikes in Iraq and one in Syria, the Pentagon said.

Eleven of the bombings in the heavy barrage targeted IS units, buildings, positions and vehicles near the strategic Mosul Dam, US Central Command, which is overseeing the air war against the jihadists, said in a statement.

The IS militants briefly held Mosul dam in August, but Kurdish forces and Iraqi army troops -- backed up by US air strikes -- succeeded in retaking the dam later that month.

The large dam in northern Iraq is a crucial piece of infrastructure and IS has repeatedly tried to seize it back.

The dam is the country's largest and, if destroyed or dismantled, it could unleash major flooding of the city of Mosul and the capital Baghdad.

A further four strikes hit near Fallujah, while others targeted Bayji, Qurayat al Hajjaj and other locations in Iraq.

These raids were carried out by US and coalition partners, using bombers, fighter jets, and unmanned drones.

The sole strike in Syria, near Kobane, destroyed an artillery piece, Centcom said, and was conducted by US aircraft.

"The destruction of ISIL targets in Syria and Iraq further limits the terrorist group's ability to project power and conduct operations," Centcom said.

Kurdish forces, backed by US air power, have been holding out against an IS offensive around Kobane for weeks.