MINGORA, Pakistan, May 3 (Reuters) - Pakistani Taliban have beheaded two government officials in the northwestern Swat Valley in revenge for the killing of two insurgent commanders by security forces, a militant spokesman said on Sunday.

Authorities struck a peace deal in February aimed at ending militant violence in the former tourist valley of Swat but the militants have refused to disarm and pushed out of the valley into neighbouring districts.

The Pakistani Taliban aggression raised alarm in the United States and in Islamabad, and a week ago the security forces launched an offensive to expel militants from two of Swat's neighbouring districts.

The two government officials were kidnapped and beheaded on Saturday evening in Khuwaza Kheil, a village 18 km (10 miles) north of the valley's main town of Mingora, said town police chief Danishwar Khan.

Their bodies were dumped beside a road.

"They beheaded the officers. We've sent an ambulance to pick up the bodies," Khan said.

Militant spokesman Muslim Khan said the beheadings were revenge for the killing of two low-level Taliban commanders earlier on Saturday.

The U.S. State Department said last week the number of people killed in terrorist attacks in nuclear-armed Pakistan last year rose by more than 70 percent over the 2007 figure.

The violence has raised fears for the prospects of the vital U.S. ally in its efforts to stabilise neighbouring Afghanistan.

President Asif Ali Zardari will meet U.S. President Barack Obama and Afghan counterpart Hamid Karzai in Washington on May 6-7 to discuss how to destroy al Qaeda and Taliban sanctuaries on the Pakistani-Afghan border [ID:nISL219917].

Obama said last week the situation in Pakistan warranted "grave concern" [ID:nSP437584].

A U.S. official said on Thursday the United States and Pakistan would likely discuss stepping up U.S. training for Pakistani security forces during Zardari's visit.

The army launched an offensive to clear militants from the Dir and Buner districts after U.S. Secretary of State Hillary Clinton accused the government of abdicating to the Taliban. [ID:nSP437584].

More than 170 militants have been killed since the offensive was launched on April 26, according to the military. There has been no independent confirmation of the military's casualty reports. (Writing by Kamran Haider; Editing by Robert Birsel and Jerry Norton)