July 18 (Bloomberg) -- Pakistan should use its army to combat terrorist groups in the tribal area bordering Afghanistan, U.S. Assistant Secretary of State Richard Boucher said, as a suicide bomber killed 13 people in an attack in Islamabad.

``Some elements have to be dealt with militarily,'' Boucher said at a briefing in Washington yesterday, according to a government transcript. ``There are groups trying to set off bombs. There are groups trying to organize attacks in other parts of Pakistan.''

Security forces last week stormed the Red Mosque, or Lal Masjid, in Islamabad, ending a standoff with Islamic clerics and killing 75 gunmen. The raid sparked anti-government protests and weekend bomb attacks on the army in the tribal region that killed more than 60 soldiers and civilians.

The suicide bomber targeted a rally before a scheduled address yesterday by Pakistan's top judge, who was suspended by President Pervez Musharraf in March. The attack was in response to the Red Mosque operation, Interior Minister Aftab Sherpao said late yesterday.

The bombing is another test for Musharraf, at a time when opposition parties are demanding he resign and Islamist groups protest his support for the U.S.-led war on terrorism. Opposition to his rule is at its strongest since he seized power in a military coup eight years ago.

``Such attacks are the backlash of the Lal Masjid operation,'' Sherpao told reporters. Whenever any action was taken during the three-month standoff at the mosque there have been similar incidents, he said.

Tribal Accord

Tribal leaders in North Waziristan at the weekend pulled out of an accord signed since 2004 to expel non-Pakistani gunmen from the region. The government said July 15 it is still negotiating with the chiefs.

``We all recognize that the agreement in North Waziristan hasn't worked,'' Boucher said in Washington. ``Because the government doesn't have direct control.''

The U.S. will help Pakistan boost its Frontier Corps ``so they become a different kind of force that's able to deal with the severe problems, but also stabilize the area'' he added.

Musharraf has deployed more than 80,000 soldiers in the tribal region and established 1,000 military posts on the 2,430- kilometer (1,510-mile) border with Afghanistan. He rejects criticism from Afghanistan that Pakistan allows Taliban and al- Qaeda fighters to train in camps in the border region and fails to stop gunmen crossing the frontier.

Appeal for Calm

Musharraf appealed to Pakistanis to remain calm and assist the authorities in their investigation into yesterday's bombing in Islamabad.

The explosion occurred about 100 meters from the stage where suspended judge Iftikhar Muhammed Chaudhry was to address a gathering of lawyers, Chaudhry Mohammed Ali, the deputy commissioner of Islamabad, said in a telephone interview. A total of 10,000 lawyers and political workers were expected to attend, GEO Television reported.

The Pakistan Bar Council called a nationwide strike for today to protest the incident, Aziz Akbar Beg, vice chairman of the council, said by telephone.

To contact the reporters on this story: Paul Tighe in Sydney at ptighe@bloomberg.net; Khaleeq Ahmed in Islamabad at

Last Updated: July 17, 2007 20:52 EDT