KABUL, Afghanistan - Afghan intelligence officials have thwarted a plot to assassinate U.S. Ambassador Zalmay Khalilzad and arrested three Pakistanis, two senior government officials said today.

The men, who were armed with rocket propelled grenades and assault rifles, were arrested in the Qarghayi district of Laghman province on Sunday, just 150 feet from where Khalilzad had planned to inaugurate a road with Afghanistan's interior minister, officials said.

One of the officials - both of whom have intimate knowledge of the investigation - said Afghan television would broadcast a video of the men in custody later today. He said the suspects had confessed to the crime and told authorities they were in Afghanistan "to fight jihad," or holy war.

Khalilzad canceled his appearance at the road opening at the last minute and was never in danger, the official said. The interior minister, Ali Ahmad Jalali, also canceled his appearance.

The men were arrested by members of the National Security Directorate after a tip that the assassination plot was in the works.

Elsewhere, fierce fighting between Taliban rebels and Afghan security forces left 18 insurgents and three others dead, a day after the U.S. military pounded suspected rebels in airstrikes that killed as many as 20.

Three U.S. troops were slightly wounded when a bomb exploded near their armored Humvee in Paktia province on Sunday, said Col. James Yonts.

Eleven rebels were killed in an hour-long firefight before dawn today after attacking a government office in Helmand province, said spokesman Haji Mohammed Wali. The district government chief and an Afghan soldier also died.

Three months of bloodshed across the south and east has left hundreds dead and sparked fears that the Afghan war is widening, rather than winding down. U.S. and Afghan officials warn things could get worse ahead of landmark parliamentary elections scheduled for September.