PESHAWAR: A roadside bomb exploded in Pakistan's northwest Thursday, killing two police officers in the latest attack on the country's security forces as they try to eliminate Taliban insurgents nesting near the border with Afghanistan.

The blast came as the Pakistani military wages a major offensive in the nearby Swat Valley, readies another in the South Waziristan tribal region, and engages Taliban fighters in other spots of the troubled region.

Security forces killed 28 militants late Wednesday in Khyber tribal region, according a statement from the paramilitary Frontier Corps. Some local tribes also have launched militias to take on the insurgents — fighting that has left dozens dead in recent days.

The U.S. believes security in Pakistan is vital to defeating the Taliban in neighboring Afghanistan and has applauded Pakistani efforts to confront the militants. But Thursday's bomb was another sign that Pakistani militants won't give up despite the rising pressure.

The bomb detonated on a road in Peshawar's outskirts, hitting a police vehicle, senior police official Ghayoor Afridi said. At least five officers were wounded. No group has claimed responsibility, but Taliban militants have carried out numerous such attacks.

Keeping Khyber militant-free is considered especially important for American interests: the region is home to the Khyber Pass, the major land transit route for fuel and other supplies headed to U.S. and NATO troops in Afghanistan.

The Frontier Corps statement gave few details of the fighting there, and did not say if any Pakistani troops died. The information is nearly impossible to confirm independently because of restrictions on journalists and the dangerous nature of the region.

Pakistan's military is pursuing operations against the Taliban with greater public support than in the past.

A poll released Wednesday said that 81 percent of Pakistanis believe the activities of the Taliban and other Muslim extremists were a "critical threat" to the country, up from the 34 percent polled on the same question in September 2007.

Socio-Economic Development Consultants in Islamabad carried out the survey for WorldPublicOpinion.org, questioning 1,000 people across Pakistan from May 17 to 28, 2009. It gave a margin of error of plus or minus