Pakistani officials say hundreds of militants have crossed from Afghanistan and attacked several border villages in Pakistan's northwest, the latest in a series of reported incursions that has raised tensions between the two countries.

Officials said militants raided villages in the Upper Dir region of Pakistan Wednesday, clashing with soldiers and local militias.

There are reports of casualties among both militants and local tribesmen, but it is unclear exactly how many people were killed or wounded. The region is largely closed to reporters and outsiders due to security and government restrictions, so information is difficult to independently verify.

Pakistan says militants allegedly coming from Afghan bases have killed more than 55 soldiers during the past month. Meanwhile, Afghanistan accuses Pakistan of intentionally firing hundreds of rockets into its territory, killing at least 36 Afghan civilians. Pakistan's military denies the allegation but says several rounds fired at militants may have landed over the border.

Taliban and al-Qaida-linked militants often cross the porous border between the two countries to carry out operations.

Elsewhere in Pakistan's northwest tribal region, Pakistani intelligence officials said troops backed by helicopters killed at least four militants in a in North Waziristan.

Officials said the battle broke out in the town of Miran Shah after the militants attacked Pakistani soldiers. Officials report that at least three militants were killed and 10 other people were wounded.

The Pakistani military has launched ground operations against the Pakistani Taliban but refuses to expand its operations at the request of Washington to attack Afghan Taliban fighters based in North Waziristan. Pakistani military officials say they want to secure gains made in other tribal regions before tackling another area.

It is unclear whether the militants killed Wednesday were Pakistanis or foreigners.