Police officials in Pakistan's volatile northwest region say an improvised explosive device detonated under a vehicle carrying troops and civilian employees of a Pakistani air force base, killing at least 13 people. VOA's Barry Newhouse reports that the attack came as political leaders in Islamabad continued a campaign to pressure President Pervez Musharraf to resign.

Pakistan's air force said the blast struck a truck carrying supplies between the Badaber air force camp and the nearby city Peshawar. Regional police commander Malik Naveed told reporters that an improvised bomb had been placed under a bridge and detonated when the vehicle passed over it.

He says it seems this could be a reaction to operations the government has launched in the tribal areas.

Since last week, the Pakistani military says troops have killed more than 100 militants in the Bajaur tribal region. The military says operations have included air strikes using jet planes and attack helicopters. Local tribal elders have reported that thousands of people have fled the fighting.  

In Islamabad, the political standoff between Pakistan's ruling coalition government and President Pervez Musharraf continued Tuesday, with the president's opponents claiming the move to oust him is gaining momentum.

On Monday, the provincial assembly in Punjab province voted overwhelmingly in favor of requesting the president to take a confidence vote. On Tuesday, Information Minister Sherry Rehman said the provincial assembly in the northwest frontier province passed a similar measure with the support of some of the president's former allies.

"This whole exercise is an exercise for a transition to democracy and a real transition to democracy. What you have seen today in the frontier province assembly is a vote of 107 against General Musharraf and only four in his favor," said Rehman.

Pakistan's other two provincial assemblies, as well as the national assembly are expected to hold similar votes in the coming days. Mr. Musharraf's opponents say those measures will build strength for an impeachment motion in Pakistan's parliament.

Some Pakistanis have taken a cynical view of the proceedings, arguing the government should instead focus on problems such as Pakistan's falling rupee, increased fuel prices and electricity shortages - instead of settling political scores.

Numan Khan, a graduate student studying business in Islamabad, says we don't understand what the leaders are doing and they can't resolve the issue in this way. He says with this confrontation we are sending the wrong message to the outside world.

Mr. Musharraf's allies say he has no plans to step down and will contest any attempt to impeach him - starting with the so-called "charge sheet" that his opponents say will list his allegedly impeachable offenses under Article 47 of the constitution. The article says a president can be impeached on a charge of violating the constitution or gross misconduct.

Legal scholars allied with Mr. Musharraf say he could ask the supreme court to rule on the validity of the "charge sheet."

Khalid Ranjha, a former law minister and current senator allied with Mr. Musharraf, says if the "charge sheet" violates Article 47, then perhaps the Supreme Court will interfere in the process.  

It is unclear how the Supreme Court could affect what would be an unprecedented attempt to impeach a president in Pakistan. The country's most powerful institution - Pakistan's military - which has repeatedly waded into political crises in the country before, has stayed silent during the current standoff.