Nato airstrikes into Pakistan from Afghanistan have killed more than 50 militants.
The helicopter attacks across the border came after the insurgents attacked a small Afghan security outpost.
Pakistan is sensitive about attacks on its territory, but an agreement allows aircraft to cross a few miles into its airspace if they are in hot pursuit of a target.
The first strike took place on Saturday after insurgents based in Pakistan attacked the Afghan outpost in Khost province, which is located right across the border from Pakistan’s North Waziristan tribal area.
The second attack came when helicopters returned to the border area and were attacked by insurgents based in Pakistan.
International and Afghan forces in the south, meanwhile, were moving into two or three areas around Kandahar city in southern Afghanistan at once to pressure the Taliban.
Shah Mohammad Ahmadi, chief of Arghandab district north-west of the city, said: “Before, when we have tried to get rid of the Taliban, when we cleaned one area we found more Taliban in a different one.” A Nato source said it had launched a “kinetic,” or combat, phase of “Operation Dragon Strike,” a joint military push with Afghan forces around Kandahar intended to rid the area of insurgents and interrupt their ability to move freely and stage attacks.
Nato said militants fought back with rocket-propelled grenades and small-arms fire.
The push in Kandahar is seen as key to the Obama administration’s strategy to turn around the nine-year war as insurgents undermine the ability of an Afghan government to rule much of the country.