A civilian helicopter crash that killed 16 people at a Nato base in southern Afghanistan pushed up the death toll yesterday in the US and allied effort to break the Taliban, adding to pressure on Washington and London.

In Afghanistan's east, a suicide bomber killed two police officers and a civilian at Torkham, an important border crossing point with Pakistan, officials said.

The US military meanwhile condemned as Taliban propaganda a video of a captured American soldier, missing since just before major new operations were launched in the south.

The video showed the soldier, named by the Pentagon as 23-year-old private Bowe Bergdahl of Ketchum, Idaho, unhurt, but saying he was scared and missed his family.

Thousands of US Marines and British troops have launched offensives in Helmand, a Taliban stronghold and the major producer of opium that funds their insurgency, as part of US President Barack Obama's new strategy to combat the Islamist insurgents.

In Kandahar, the Taliban's birthplace adjacent to Helmand, Captain Ruben Hoornveld, a Dutch Nato spokesman, said there was no enemy involvement in the crash which occurred as the helicopter was taking off at the sprawling Kandahar Air Field.

Russia's Interfax news agency described the helicopter as an Mi-8 transporter, operated by a Russian firm, and said it had 17 passengers and three crew on board. It put the death toll at 15.

The nationalities of those killed were not immediately known.

It was the second crash involving a Soviet-era helicopter in a week. Six Ukrainian crew members died when an Mi-26 transport helicopter crashed in Helmand on Tuesday.

Nato and US forces rely heavily on aircraft for troop and cargo movement in a country where travel by road is difficult. They occasionally hire cargo aircraft from former Soviet states.

July has already become the deadliest month of the eight-year-old-war for foreign troops, putting pressure on political leaders in Washington and London. Commanders have said President Obama's new strategy and his decision to pour in thousands more troops this year would lead to a spike in casualties.

Civilians have also been suffering at record levels. The suicide bomber attack on the Torkham border post was the second deadly attack on the post in three weeks.

With Britain suffering its worst battlefield casualties since the Falklands War in the 1980s, political leaders recognise that patience at home is running thin. Britain has lost at least 185 soldiers in Afghanistan - more than during the Iraq war.