There were so many flaws in President Barack Obama's midweek announcement about the US military response to the threat posed by the Islamic State (IS) that it is easy to understand his earlier hesitation in divulging his new policy.

As we have come to expect, his 14-minute address to the nation from the White House was strong on rhetoric. He talked about the need to "degrade and ultimately destroy" IS fighters, likening them to a spreading cancer, and he warned them that "if you threaten America, you will find no safe haven".

So far, so typical, but behind the firm words there are more questions than answers. Obama's new military policy is predicated on the indirect approach - using precision air strikes to hit IS targets in Iraq and Syria while giving arms and training to proxy forces in the shape of Kurdish peshmerga forces, the Free Syrian Army and Iranian-backed Shia militias.

At the very most he will order the deployment of 475 US military specialists northern Iraq and eastern Syria to begin the process of equipping and training fighters in the field to engage the IS. Military sources in Washington insist that there will be "no boots on the ground" but become coy when asked if the teams will include forward air controllers who are usually essential for the execution of precision bombing operations.

In taking this option, Obama is attempting to make good his second-term promise that he will not oversee any further US expansionism in the global war against terror. Under his watch, US forces have withdrawn from Iraq and are already pulling out of Afghanistan; he also refused to become embroiled in Libya and Syria but only by the skin of his teeth through the UK Parliament's refusal to endorse aerial operations against the latter country. Treading that line has not been easy and in the past fortnight he has been under pressure to retaliate following the execution of two US journalists. However, it is a moot point if the current tactics will be any more successful than those pursued by his Democrat predecessor Bill Clinton, who ordered punitive cruise missile raids against Saddam Hussein's Iraq in the 1990s.

While the use of air strikes will placate those who are opposed to further military involvement in the Middle East, the new policy is inherently dangerous. As missile-firing drones have shown in Afghanistan and Pakistan, targets can be wrongly identified leading to civilian casualties and this causes outrage in the wider civilian population. If that happened in Iraq or Syria it would not be a deterrent to IS but would undoubtedly encourage a new generation of jihadis

There is also the danger of US aircraft being shot down. Although IS does not possess sophisticated ground-to-air missiles, Syria does in the shape of recent equipment supplied by Moscow and there are no guarantees that president Bashar al-Assad will sit by idly if US warplanes attack his country. The last thing needed by the White House would be a downed bomber with its crew being paraded as prisoners or perhaps even facing public execution if they are captured by IS fighters. Yesterday, the Syrian government announced that any US air strikes within their air space would violate international law and this was backed up by Russia whose foreign ministry demanded that the issue be passed to the UN Security Council.

On the face of it, arming proxy forces is a more attractive option but it too is not without dangers. While the Kurdish peshmerga forces are disciplined and well trained they have a tendency to fight for their own goals and do not always consider the wider picture. During the recent fighting for the Mosul dam which drove away IS forces in northern Iraq there was a distinct impression that US warplanes were acting as a Kurdish air force. That might not create any longer-term problems but the same cannot be said if it ever seems that the US is supporting pro-Shia forces funded by Iran. Already there have been reports that the regime in Tehran has ordered its elite Quds force to engage IS fighters in northern Iraq and while that squares with Obama's intention of ridding the area of Sunni extremism it does not fit well with US policy of forcing Iran to reveal full details about its nuclear policies.

Obama at least got one thing right in making his long-awaited announcement. Unlike his predecessor George W Bush, who revelled in his role as the avenging president, he came across as a reluctant warrior who is taking these steps with a heavy heart and a full determination not to commit US ground forces to the fight. In that respect it was hugely significant that his statement was made on the anniversary of the September 11 attacks in 2001.