Barack Obama has said the US is "on track" to achieve its goals in Afghanistan, following publication of the US annual strategy review.

美国年度战略报告上，奥巴马称美国在阿富汗所期望取得的成果即将“走上正轨”。

The review said al-Qaeda's leadership was at its weakest since 2001.

And it added that the US had made enough progress to start a "responsible reduction" of forces in July 2011.

Mr Obama said US forces and their allies were clearing more areas from Taliban control, but warned that the gains were still fragile.

"This continues to be a very difficult endeavour（尽力，竭力） ," Mr Obama said. But he added that US would remain "relentless¹（无情的，残酷的） " in pursuit of（寻求，追求） al-Qaeda.

The review says the surge in foreign troops has succeeded in halting Taliban momentum² in much of the country, but BBC correspondents say the bigger picture is of an insurgency（叛乱，暴动） fighting to the death in Helmand and Kandahar and expanding in places like Ghazni and Kunduz.

'Wider insurgency³'

The US plans to end combat operations in 2014 and transfer responsibility for the country's affairs to Afghans.

The White House review comes at a time when civilian⁴ casualties are at their highest since the US-led invasion of 2001. This year has also been the bloodiest⁵ for foreign troops since 2001, with the US taking the brunt（冲击） of the casualties.

At the White House, Mr Obama said he wanted to remind Americans that America was in Afghanistan to disrupt, dismantle⁶（拆除，解散） and defeat al-Qaeda.

"It was Afghanistan where al-Qaeda plotted the 9/11 attacks that murdered 3,000 innocent people. It is the tribal⁷ regions along the Afghan-Pakistan border from which terrorists have launched more attacks against our homeland and our allies.

"And if an even wider insurgency were to engulf⁸ Afghanistan, that would give al-Qaeda even more space to plan these attacks."

He said al-Qaeda's leadership was "hunkered down", but said it would continue to take time to defeat an enemy he described as "ruthless and resilient".