KABUL (AFP) Nine NATO soldiers were killed in militant attacks and a helicopter crash in Afghanistan Monday, the second deadliest day this year as US-led troops build an ambitious campaign against the Taliban. Three Australian commandos and a US soldier were killed when their helicopter crashed in southern Kandahar province the single worst loss of life for the Australian military in the nearly nine-year Afghan war. Another two NATO troops, including an American, died in separate bomb explosions elsewhere in the south, the powerbase of the Taliban militia that is fighting an increasingly deadly insurgency against Western troops. Three more American soldiers were killed in other militant attacks, a spokesman for the NATO-led International Security Assistance Force (ISAF) told the agency. One US soldier died following a small-arms attack in the south and the two others died after a roadside bomb attack in the east. On top of the deadly day, London announced that 300 British troops had now died in Afghanistan after a soldier died from wounds suffered in an explosion earlier this month in the southern province of Helmand. The incidents brought to 64 the number of NATO soldiers killed in the Afghan conflict this month, and to 284 the number so far this year, according to an AFP tally. Australia, which said the helicopter crash was not caused by enemy fire, also mourned. This is a tragic day for Australia and the Australian Defence Force, Prime Minister Kevin Rudd told parliament. This is a very heavy price to pay. It was the second helicopter incident to kill NATO troops this month. Taliban militants killed four US soldiers on June 9 when they shot down a helicopter in Helmand. British Prime Minister David Cameron, who visited Afghanistan earlier this month, said British troops would leave as soon as they (Afghans) are able to take care and take security for their own country. Another family with such grief and pain and loss. Of course the 300th death is no more or less tragic than the 299 that came before, he said.