At the same time, Taliban militants have ended a 10-month ceasefire agreement with the government along the Afghanistan frontier.

An estimated 38 people were killed yesterday in at least two separate attacks, though there was confusion about the details. At least 80 people were wounded. In addition, 24 troops were killed in another incident on Saturday.

General Pervez Musharraf's government had been expecting violence, after militants made threats to seek revenge for the military operation to clear Islamabad's Lal Masjid, or Red Mosque, last week in which at least 80 students died.

Thousands of additional troops have been deployed in the north-west of the country, but it is unclear whether they are providing additional targets for the militants.

Officials said that three blasts struck a military convoy in Swat, a mountainous area of North West Province, killing 11 troops and seven civilians and wounding 47. Reports said two vehicles laden with explosives had rammed the convoy.

In the day's second attack, a suicide bomber targeted scores of people taking exams for recruitment to the police force in the city of Dera Ismail Khan. The blast killed 20 people and wounded 35, said police officer Mohammed Aslam.

The attacks followed the death of 24 paramilitary soldiers, who were killed in a suicide car bomb attack in North Waziristan on Saturday. Officials said this was the most serious single attack on security forces since last November.

After the military operation at the Lal Masjid on 10 July, General Musharraf delivered a televised address in which he said extremism would not be tolerated anywhere in Pakistan.

But while the President received considerable public support for his decision to take action against militants at the mosque, he was already facing genuine political problems and has little time or resources for a battle with extremists.

Should he seek to impose martial law - something about which there has already been speculation - he would further lose support among the professional classes, many of whom have been outspoken in their support of the country's former Supreme Court Chief Justice - seemingly ousted by Mr Musharraf for political reasons.A decision on a legal appeal by the Chief Justice is expected to be announced this week.

Reports suggest the decision by Taliban in North Waziristan to end a ceasefire agreement was not linked to the Red Mosque operation. Under the pact, authorities agreed to stop operations against militants in return for their pledge to not send fighters into Afghanistan or to launch attacks on security forces.

While the US said the agreement had not stopped raids into Afghanistan, it had led to a sharp fall in attacks on Pakistani forces in North Waziristan.

* Osama bin Laden praised martyrdom in a new videotape posted on a militant website yesterday .

The clip, which lasted less than a minute, was undated and part of a 40-minute video showing al-Qa'ida fighters in Afghanistan.

Bin Laden is heard glorifying those who die in the name of Jihad, or holy war, saying even the Prophet Mohamed "had been wishing to be a martyr".