A bid by Islamic State fighters to seize the flashpoint Syrian border town of Kobane has stalled, American officials say, with the help of air strikes reported to have killed over 500 jihadists.  US and allied aircraft have flown nearly 6600 sorties in the air war against the Islamic State (IS) group and dropped more than 1700 bombs, the American military said on Thursday.  The latest tally was released one month after the US-led coalition extended its air campaign from Iraq into Syria in a bid to counter the advance of the jihadists.  The effect of the open-ended air campaign remains the subject of debate, with the White House saying the militants have been damaged by the strikes, but critics pointing to the group's battlefield successes despite the raids.  In Washington, Pentagon chief Chuck Hagel acknowledged "mixed" results in the war effort but said: "We believe that our strategy is working."  IS, which declared in June a "caliphate" over territory it seized in Iraq and Syria, was meanwhile described as the world's wealthiest "terror" group, earning $1 million a day from black market oil sales alone.  The Kurds in Kobane, which has become a crucial battlefield for both the IS jihadists and their opponents, have been holding out for more than a month, buoyed by a promise of Iraqi Kurd reinforcements and by US air drops of weapons.  "I think the Kurdish defenders ... are going to be able to hold," a defence official at US Central Command said, speaking on condition of anonymity.  Kurds say their fighters are exhausted and anxious for promised reinforcements from Iraq's autonomous Kurdish region.  MPs there have agreed to send their peshmerga fighters after Turkey said it would allow 200 of them to travel through its territory to Kobane, where IS has an estimated 1000 militants.  On the ground, the jihadists made fresh advances in and around Kobane, said the Syrian Observatory for Human Rights.  The IS group had also taken control of a string of villages west of Kobane, after days of trading territory with the Kurds.  US military officials delivered sobering news from Iraq, saying the Iraqi army is still months away from staging a major offensive to retake ground lost to the IS jihadists and is regrouping after suffering battlefield defeats this year.  Iraqi security forces are currently able to stage small-scale attacks against the IS group, but need time to plan and train for a larger operation, even with the aid of US-led air strikes, one military official told reporters.  "It's well within their capability to do that (counter-attack), on the order of months, not years," said the official.  But he added: "It's not imminent."  The Iraqi capital Baghdad has also seen a wave of bomb attacks against Shi'ite targets in recent days, with IS militants claiming responsibility for some.  The month-old US-led aerial campaign on Syria has killed 553 people, all but 32 of them jihadists mostly drawn from overseas, the Observatory said.  The jihadist toll included 464 IS militants and 57 fighters from the al-Qaeda affiliated Al-Nusra Front, said the Britain-based Observatory, which relies on a wide network of sources inside Syria.  Do you have any news photos or videos?
After first focusing on Iraq, the American-led coalition has dramatically expanded its air strikes in Syria recently, including in Kobane.