WASHINGTON (CNN) -- Insurgents fired simultaneously on Pakistan and Afghanistan positions Thursday night in hopes of provoking a battle between the two military forces, NATO officials said Friday.
A U.S. Marine jokes with an Afghan Border police officer near Helmand Province on Friday.
U.S. forces were called into action on the Afghanistan-Pakistan border after Afghan security forces came under fire from insurgents inside Pakistan, NATO said. Meanwhile, two Pakistani border outposts also had come under fire.
Six mortar rounds hit one Pakistani outpost, and troops there returned fire, according to Pakistan military spokesman Maj. Gen. Athar Abbas.
Six Pakistani security personnel were injured in the exchange along the South Waziristan border, and a number of casualties were "observed/reported" on the other side of the border, he said.
NATO said it had reports that four Afghan border police officers and eight Pakistani military members were wounded in the four-hour firefight.
International Security Assistance Force officials "suspect that the insurgents' dual attack was specifically intended to spark a border incident," the statement said. ISAF is the NATO contingent in Afghanistan.
U.S. forces first responded with artillery fire. U.S. officials with knowledge of the firefight said all rounds landed inside Afghanistan, within 350 meters (383 yards) of the border.
As the firefight continued, a U.S. F-15 aircraft dropped a GBU-13 bomb that also landed in Afghanistan, the officials said.
CNN's Reja Sayah contributed to this report.