KABUL/ISLAMABAD: Insurgents shot down a NATO helicopter and killed four American troops in southern Afghanistan on Wednesday in the latest bloodshed ahead of a major operation in the militants’ heartland, the military said.

In another unprecedented assault near Islamabad, gunmen attacked military vehicles and goods destined for NATO troops in Afghanistan, torching over 60 trailers and killing seven people, police said Wednesday.

US military spokesman in Kabul, Lt. Col. Joseph T. Breasseale, confirmed the four troops killed were Americans.

Helmand provincial spokesman Daoud Ahmadi said the helicopter was shot down about midday in Sangin district during an operation involving NATO and Afghan security forces.

Top Taleban spokesman Qari Yousef Ahmadi said the insurgents shot off two rockets to down the helicopter.

The downing of the chopper came as Afghanistan’s ousted intelligence chief warned  that Afghan President Hamid Karzai’s strategy of seeking reconciliation with the Taleban was dangerously flawed.

The deaths, and that of a British soldier killed by an improvised bomb in a separate attack Wednesday, take NATO’s toll to 29 deaths in nine days, according to an AP count.

The overnight attack on trucks was the first on NATO supplies so close to the Pakistani capital and entailed one of the biggest losses on the convoys, whose presence is bitterly opposed by Taleban and Al-Qaeda-linked elements. A dozen gunmen stormed the depot on the outskirts of Islamabad en route to the northwestern city of Peshawar and toward the NATO supply route into Afghanistan, where 130,000 US-led foreign troops are fighting the Taleban.

Although militants have routinely attacked supplies for US and NATO-led foreign forces traveling through Pakistan, the audacious assault will raise questions about insecurity on the doorstep of the heavily-guarded capital.

Rows of tankers and trucks, including a dozen loaded with military vehicles, were reduced to a twisted mass of metal after the inferno at the Tarnol depot was brought under control, an AFP photographer said.

“There were 60 trailers gutted by fire. In addition 80 NATO vehicles were partially damaged,” Shah Nawaz, police station chief in Tarnol, said. “Seven people, most of them drivers and their helpers, were killed.”

Police were conducting a full-scale investigation into the incident while the government demanded a report into the incident within three days.

“The important question to ask is how were they moving in such a big convoy under the current environment when trucks with NATO supplies are routinely attacked,” said Nawaz. Police official Qadeer Ahmad confirmed the casualties and said 40 trailers, which had been mounted on trucks, were destroyed in the inferno.

Government officials blamed that attack on Punjab-based militants, who are thought to have forged growing links with Taleban based in the northwest.