At least six people have died in an overnight clash between Pakistani security forces and insurgents operating near the border with Afghanistan.

A five-hour battle erupted in the Bajaur tribal area of northwestern Pakistan late Tuesday night, after a security vehicle on patrol was hit by an improvised roadside bomb. Military personnel exchanged fire with a group of unknown militants armed with rocket launchers and light weapons.

At least six people were wounded in the fighting. The identity of the victims was not announced.

In other news, Pakistani authorities are investigating who organized a double suicide bombing in Lahore that killed at least 30 people.

No one has claimed responsibility for Tuesday's car bombings, but authorities said Wednesday they were similar to other attacks carried out by al-Qaida and Taliban-linked militants.

The government placed Pakistan on high alert Tuesday, increasing security in public areas and at government installations across the country.

The first bomb was the most deadly - killing more than 20 people and tearing the facade off the federal police building in downtown Lahore.

The second attack killed four people, including two children, in a residential neighborhood near the home of political leader Asif Ali Zardari.

Pakistani President Pervez Musharraf and United Nations Secretary-General Ban Ki-moon condemned the bombings - the latest in a wave of attacks in Pakistan.

At least 600 people have been killed over the past year. Most attacks have taken place in the tribal regions along the border with Afghanistan, but violence blamed on Islamist militants is spreading across the country.

Some information for this report was provided by AFP.