The militants, the sources said, had attacked Combat Outpost Narizah, an Afghan base eight miles from the Pakistani border in Tani district of Khost.
US forces repelled the attack and pursued the militants to their post just across the border in North Waziristan.
“An air weapons team in the area observed the enemy fire, and following Inter-national Security Assistance Force rules of engagement, crossed into the area of enemy fire,” the International Security Assistance Force stated in a press release.
“The Isaf aircraft then engaged, killing more than 30 insurgents.”
Isaf confirmed that the helicopters struck at the Haqqani Network fighters in Pakistan.
The attack helicopters launched their attack “after following the proper rules of engagement under inherent right of self-defence,” Master Sergeant Matthew Summers, a public affairs official, told reporters.
On Saturday, Isaf launched a second attack against the Haqqani Network, after taking fire in the border area. “Several additional insurgents” were killed in that attack.
The assault on Combat Outpost Narizah is the sixth against outposts in eastern Afghanistan since the end of August.
The US claims that the Haqqani Network is based near Miramshah in North Waziristan, and has close ties to Al Qaeda and other Pakistani and Central Asian militant groups.
US officials say that Isaf forces are permitted to pursue Taliban forces across the border if they are engaged in fighting or are under attack.
They said that US and Pakistani military commanders have agreed to a set of rules for hot pursuit, which says that US forces must be engaged with the Taliban or Al Qaeda as they cross into Pakistan.
US forces, however, not penetrate more than six miles into Pakistani territory.
But they can go deeper inside Pakistan if they identify the location of Osama bin Laden, Ayman al Zawahri, or Mullah Omar.
Pakistan denies having such an agreement while US officials refuse to offer on the record comments on this issue.
Source: DAWN