A suspected U.S. missile strike killed a purported foreign militant Thursday in a Pakistani tribal area considered a haven for the Taliban and Al Qaeda, while a homicide bombing left four security personnel dead, officials said.

In another sign of how violence and economic problems are shaking confidence in the nuclear-armed country, Pakistan's currency slumped to an all-time low against the United States dollar.

The missile strike hit a house in the South Waziristan region of Pakistan's wild border belt, considered a likely hiding place for Al Qaeda leaders Osama bin Laden and Ayman al-Zawahri.

Two Pakistani intelligence officials told The Associated Press that reports from informants and field agents suggested one foreign militant died in the attack and that another foreigner was injured.

Asked if any Al Qaeda leaders had been hit, the officials said that Arabs had been living in the house but the identities of the victims were not yet clear. They said foreign and Pakistani militants had frequented the house in a remote, forested area since its owner fled the tribal region last year.

Both officials spoke on condition of anonymity because they were not authorized to brief the media on the record.

A local resident, Javed Mehsud, said he saw a number of unmanned planes in the sky before and after three explosions destroyed the house in the village of Tapargai.

"I could see smoke rising but nobody dared go to look because the spy planes were still over our area," he said by telephone.

U.S. military and CIA drones that patrol the frontier region are believed to have carried out at least a dozen missile strikes against suspected militant targets since August.

The U.S. rarely confirms or denies involvement in the attacks which have intensified amid frustration in Washington at the escalating insurgency in neighboring Afghanistan.

All of the recent strikes, as well as a highly unusual raid by helicopter-borne commandos, have been in the regions of North and South Waziristan, key strongholds for Islamic militants fighting on both sides of the border.

With Pakistan's army also stepping up operations in its volatile northwest, militants have responded with a sequence of bloody homicide attacks, including last month's truck bombing of Islamabad's Marriott Hotel.

Thursday's blast wrecked a police station in Swat, a picturesque valley where fighting has raged for more than a year.

Police said insurgents opened fire on their station in Mingora, Swat's main town, after midnight with guns and rockets before the bomber detonated an explosives-laden vehicle next to the police compound.

District police chief Dilawar Bangash said one officer and three paramilitary troops died and another 26 people were injured, many of them seriously.

Meanwhile, security forces backed by tanks and warplanes opened a second major front in the nearby tribal region of Bajur in August.

However, there are doubts about whether Pakistani security forces can defeat the militants without inflicting heavy civilian casualties and eroding support for the country's pro-Western government.

Western governments worry that Al Qaeda is regrouping in the border zone and that would-be terrorists from Europe and North America are going there to receive training.

Pakistan's political and security problems are deterring foreign investment and exacerbating the country's economic problems, which include runaway inflation and slowing growth.

On Thursday, the Pakistani rupee dropped to more than 82 to the dollar, continuing a slide that has seen it lose more than 30 percent of its value this year.