Afghanistan ? Militants attacked government offices and a police convoy Saturday, continuing a series of assaults that has left at least 41 people dead in the region over two days, government officials said.

About 250 Afghan forces fought more than 200 rebels in the area’s fiercest fighting in months. At least 19 people were killed in Afghanistan and Pakistan on Saturday.

Afghan officials said U.S. forces joined the battle Friday and Saturday, but a U.S. military spokesman said he could only confirm involvement in the first day of fighting.

The violence spread across the border as a roadside bomb exploded by an army vehicle Saturday in Pakistan in a tribal region near Afghanistan, killing three security personnel, an official said.

Nobody immediately claimed responsibility, but security officials have blamed al-Qaida-linked Islamic militants for previous attacks in the area, where Pakistan has sent thousands of troops to flush out insurgents.

Fighting began Friday with a mountain ambush of a police convoy that left 16 militants and six police dead and scores wounded, said Amir Mohammed Akhund, the province’s deputy governor.