An Afghan boy looks on as his father is searched by an Afghan National Army soldier during a patrol with United States Marines near Musa Qaleh, in Helmand province. Photo / AP

An Afghan boy looks on as his father is searched by an Afghan National Army soldier during a patrol with United States Marines near Musa Qaleh, in Helmand province. Photo / AP

A crowded bus hit a roadside bomb in Helmand province in southern Afghanistan yesterday, killing 25 passengers.

At the same time, Nato continued to investigate claims that a helicopter gunship mistakenly opened fire on a house packed with civilians, with Afghan Government officials saying that 52 people were killed.

If verified, the attack would be the coalition's worst civilian casualty incident for over a year.

Meanwhile, WikiLeaks editor-in-chief Julian Assange claims his organisation does not know who sent it some 91,000 secret US military documents, saying the website is set up to hide the source of its data from those who receive it.