Two U.S. soldiers were killed in a firefight with insurgents Monday, while an Afghan vice president escaped a bomb attack on his convoy in the latest assassination attempt on a political leader ahead of key elections.

The U.S. military said leaders of Al Qaeda (search) and the Taliban (search) have held a series of meetings in Pakistan to discuss how to disrupt the elections. U.S. and Afghan officials have been warning of increased violence before the Oct. 9 presidential vote.

Monday's violence followed a failed assassination attempt last week on U.S.-backed interim President Hamid Karzai (search), considered the favorite to win the election.

The Americans were killed in a clash with militants in the troubled southeastern province of Paktika, the military said. The dead were not immediately identified.

Two other Americans were slightly wounded and six Afghan government troops were taken to a U.S. base for treatment, a military statement said.

According to the Defense Department, 137 U.S. military personnel have died in Operation Enduring Freedom, launched after the Sept. 11, 2001, attacks in the United States. Some 99 of the fatalities have been in or around Afghanistan (search), and 54 of them have been troops killed in action.

In northern Afghanistan, Nayiamatullah Shahrani, one of the country's four vice presidents, and a Cabinet minister were on route to to inspect a road project when their convoy struck the bomb in the Khanabad district of Kunduz province.

The bomb, hidden by the roadside, was detonated by remote control and damaged a car carrying Shahrani's bodyguards in the 20-vehicle convoy, Police Chief Mutaleb Beg said.

"It damaged one of the cars and one of his guards was slightly hurt by the flying glass," he said. Beg blamed "enemies" for the attack, but didn't elaborate. No one was arrested.

Shahrani and Urban Development Minister Gul Agha Sherzai, who was also in the convoy, were unharmed and continued to Takhar province.

On Thursday, Karzai aborted his first major campaign event when suspected Taliban fired a rocket at the U.S. military helicopter bringing him to a school opening in southeastern Afghanistan.

The American deaths came amid a flurry of reported attacks on U.S. troops across the troubled south and east of the country, where Taliban-led insurgents are most active.

The military statement said that in Zabul province, close to the Pakistani border, U.S.-led forces killed several militants in a clash north of Qalat, the provincial capital.

Coalition forces also came under fire near Deh Rawood, a town in Uruzgan province where American forces have a base. U.S. and Afghan troops also came under fire in another skirmish Monday, injuring one of the Afghans, the statement said.

More than 900 people have died in political violence across Afghanistan this year, and officials are braced for more. Election workers have also been directly targeted, with 10 killed so far, but the violence has failed to prevent millions of Afghans from registering to vote.

Maj. Scott Nelson, a U.S. military spokesman, said "relatively high-ranking" members of Al Qaeda and the Taliban — as well as rebel Afghan faction Hezb-e Islami, led by Gulbuddin Hekmatyar — have held several meetings in Pakistan on how to derail the vote.

Citing intelligence reports, Nelson said the participants were also discussion how to deal with increasing crackdowns on both sides of the Afghan-Pakistani border to root out their activities.

The Pakistani government said the idea that such meetings could have taken place on its territory was "baseless."

"Al-Qaida and remnants of the Taliban regime are on the run in Pakistan. They cannot hold conferences," Foreign Ministry spokesman Masood Khan said in Islamabad.

The U.S. military was "looking in the wrong direction," he said. "The real danger lies inside Afghanistan" from warlords, drug traffickers and insurgents.

Nelson said it was "certainly" possible that Usama bin Laden (search) and other leaders of Al Qaeda were in the rugged border region — on either side of the porous border.

Maj. Gen. Eric Olson, the operational commander of the U.S.-led force in Afghanistan, said this month that he had no fix on where bin Laden or his deputy, Ayman al-Zawahri, were located.

But he said he believed the Al Qaeda leaders were still pulling some of the strings in the stubborn Afghan insurgency.

Olson cited a car bombing that killed about 10 people, including three Americans, at the office of a U.S. security company in Kabul last month. He said a splinter group of Al Qaeda with Pakistani and Afghan members may have been responsible.

Thousands of Pakistani forces have carried out bloody offensives in the Waziristan tribal region next to the border, bombing a suspected training camp and killing scores of suspected militants.

Nelson said U.S.-allied forces had intensified their campaign against militants in the neighboring Paktika, Paktia and Khost provinces of Afghanistan.