Kabul - At least 16 civilians were killed on Sunday when a helicopter crashed near a military base in southern Afghanistan, the NATO-led force said, in the second fatal chopper crash here in a week.

    The civilian-contracted aircraft was not shot down by insurgents, the NATO-led International Security Assistance Force (ISAF) said, but gave no details on what caused the crash in war-torn Kandahar province.

    "ISAF can confirm that 16 civilians have been killed in the helicopter that crashed earlier today (Sunday) in Kandahar province," the statement said.

    "There are an additional five casualties whose condition is yet to be confirmed... Emergency personnel are still on the scene. No military personnel were amongst the casualties.

    "There was no indication of the cause of the accident but insurgent action has been ruled out."

    ISAF earlier said that the crash happened on take-off from Kandahar Airfield, part of the biggest US military base in southern Afghanistan.

    It gave no details on the nationalities of the casualties or the contracting company, but Russian news agencies reported that the aircraft was an MI-8 helicopter belonging to Russian company Vertikal-1.

    The helicopter carrying 17 passengers and three crew members crashed during take-off, the agencies said, citing the Russian Federal Air Transport Agency.

    Authorities were establishing nationalities of the dead and injured passengers, Interfax agency said. A representative of the Russian Federal Air Transport Agency declined to comment when contacted by AFP.

    The United States and NATO-led forces battling a fierce Taliban-led insurgency in Afghanistan frequently rely on civilian helicopter companies to ferry goods and personnel out to more remote areas of the country.

    Last Tuesday, a civilian helicopter crashed in southern Helmand province while transporting contractors, killing six passengers and a child on the ground, NATO and local officials said.

    The Taliban claimed that they brought down the chopper but it was difficult to independently verify the claim.

    There are about 90,000 international troops, mainly US, British and Canadian, deployed in Afghanistan to help Kabul fight the Taliban insurgency which followed the 2001 US-led invasion to oust their regime.

    Afghanistan has seen a surge of violence in recent weeks, as the country prepares to go to the polls for landmark presidential and provincial council elections on August 20.

    With the nearly eight-year insurgency at its deadliest, the United States has dispatched up to an extra 21,000 soldiers to try to stabilise the country ahead of the vote.

    Military casualties have surged in recent weeks as about 4,000 US Marines and thousands of British and Afghan forces battle their way into Taliban strongholds in the south in separate assaults launched about three weeks ago.