PESHAWAR, Pakistan - Gunmen kidnapped an Iranian diplomat after killing his guard Thursday in Peshawar, authorities said, a day after an American aid worker was shot dead in the city in Pakistan's volatile northwest.

The kidnapping was the latest in a string of attacks on foreigners in the region and underscored deteriorating conditions in a region used by al Qaeda and Taliban militants as a staging ground for assaults on U.S. and NATO forces in Afghanistan.

Neither U.S. missile strikes on insurgent targets nor aid efforts in the region appear to have had much impact on stemming the violence.

The Iranian diplomat was driving over a narrow bridge when two armed men blocked his way with their white car and opened fire, said Banaras Khan, a police investigator in Peshawar who cited a witness. He said the Pakistani guard was killed and the attackers dragged the Iranian into their vehicle before fleeing.

Officials identified the diplomat as Heshmatollah Atharzadeh, a commercial attache in Peshawar. Iran's Foreign Ministry spokesman Hasan Qashqavi denounced the abduction as a "terrorist act," according to Iranian state media.

Pakistan's foreign ministry also condemned the attack, for which there was no immediate claim of responsibility, and promised that authorities would take "all necessary measures" to recover Atharzadeh.

Iran and Pakistan are Muslim nations and neighbors who have generally had cordial relations. Still, majority Shiite Iran opposed the hardline Sunni Taliban regime in Afghanistan in the 1990s, while Pakistan supported it. Iran is also an adversary of the U.S., while Pakistan is a close ally of Washington.

Until recently Peshawar, the dusty, sprawling regional capital, was considered relatively safe for foreigners. But residents say criminality as well as militancy appears to be on the rise. It was possible the Iranian was kidnapped for a ransom.

The latest kidnapping happened in the same area where Afghanistan's ambassador-designate was taken in September and his driver killed. The Afghan diplomat is still missing, as are a Chinese engineer and a Polish surveyor who also were kidnapped in the northwest.

On Wednesday, U.S. efforts to help reduce militancy in Pakistan's northwest through development programs were dealt a blow when gunmen shot and killed American Stephen Vance, who worked for CHF International, a U.S.-based aid group.

The group was implementing U.S. government-funded programs to pump $750 million over five years into developing basic infrastructure such as wells and better clinics and roads in the impoverished tribal areas bordering Peshawar.

Vance was attacked as he was being driven from his home to his office in University Town, an upscale area of Peshawar where a top U.S. diplomat narrowly escaped a gun attack a few months ago. Vance's Pakistani driver also was killed.

The northwest's semiautonomous tribal regions are considered possible hiding places for Osama bin Laden and al Qaeda No. 2 Ayman al-Zawahri. Militants use pockets of the northwest as staging grounds for attacks on U.S. and NATO troops in Afghanistan.

The U.S. has stepped up missile strikes on militant targets in the tribal areas, prompting protests from Pakistani leaders.

During a visit to New York on Wednesday, Pakistan's foreign minister warned against the missile strikes, calling them "unproductive."

"They are contributing to alienation as opposed to winning people over," Shah Mahmood Qureshi said.