Policemen die in blast in Pakistani city of Peshawar

At least three policemen have been killed and four others injured in an explosion in the north-western Pakistani city of Peshawar, police say.

The blast occurred when the vehicle carrying them hit a roadside bomb.

It came hours after a bomb attack outside a court in the city killed 20 people and injured more than 40 others.

Attacks across Pakistan have increased dramatically as the army continues its offensive against the Taliban in South Waziristan, near the Afghan border.

The police patrol hit the roadside bomb shortly after midnight on Thursday, the police said.

"It was a remote-controlled bomb. Two policemen died on the spot, while a third has succumbed to his injuries a short while ago," police official Mohammad Haroon told Reuters news agency.

Separately the death toll in Thursday's bomb attack outside the court in Peshawar has risen to 20, following the death of one of those injured.

Officials said a suicide bomber had carried out that attack.

Spike in violence

Peshawar, near the Afghan border, has been targeted repeatedly in recent months.

Last Friday, a suicide car bomb attack on the office of Pakistan's main intelligence agency ISI on the same road as the court building killed at least 12 people and injured 40 others.

And on 28 October, at least 100 people were killed when a huge car bomb ripped through Peshawar's busy Peepal Mandi market.

The city's Pearl Continental Hotel was also targeted by a truck bomb earlier this year.

The attacks come as Pakistan is carrying out an offensive in South Waziristan, which is considered to be one of the main sanctuaries for Islamic militants outside Afghanistan.

Security has been stepped up across Pakistan, but correspondents say the government still appears to be unable to stop the attacks.