BAGHDAD — A suicide bomber blew himself up Thursday in a crowd of police recruits in northwestern Iraq, killing at least 16 men and wounding 14 others, an official said.

The blast occurred in Sinjar, a town near the Syrian border that was the site of the deadliest attack of the war — a series of suicide truck bombings that killed an estimated 500 people.

Nobody has claimed responsibility for the latest attack. But it bore the hallmarks of al-Qaida in Iraq, underscoring Iraqi claims that insurgents have fled from Mosul to remote areas to escape a U.S.-Iraqi offensive under way in that city, about 75 miles east of Sinjar.

The top official in Sinjar, Dakhil Qassim, said the casualties would have been higher, but the security services had received tips that police recruiting centers would be targeted and had issued a warning on Wednesday advising people to stay away.

Police closed the recruiting center due to the threat, but a crowd of desperate jobseekers still gathered at the center in Sinjar. Those killed included 14 recruits and two policemen, while 14 other people were wounded, Qassim said.

"We told them that there (was) no more recruiting for security reasons," Qassim said. "But people gathered at recruiting center anyway hoping that some official might register their names."

Despite the risks, jobs in the police force are prized in areas of the country where unemployment runs high.

Sinjar is dominated by Yazidis, a small Kurdish-speaking sect whose members are considered to be blasphemers by Muslim extremists.

The U.S. military blamed al-Qaida for the Aug. 14 bombings that devastated nearby villages and killed some 500 people.

U.S. and Iraqi forces have met relatively little resistance during the operations in Mosul, although there have been sporadic attacks. Commanders have said they believe insurgent leaders had fled to neighboring areas and would try to regroup.

U.S.-allied Sunni fighters acting on tips that insurgents were trying to sneak from Mosul to Baghdad found 12 gunmen hiding inside the tank of an oil truck with a driver who was wearing an explosives belt.

The militants were killed after clashes broke out and the driver blew himself up, according to a police official who read the report but spoke on condition of anonymity because he wasn't authorized to release the information.

Another suicide bomber driving a police vehicle struck Iraqi commandos earlier Thursday in Mosul, killing three of them and wounding nine other people, according to battalion commander Capt. Aziz Latif.

The victims were from a unit sent from the southern city of Kut to participate in the Mosul crackdown, Latif said.

Gunmen in Baghdad lobbed grenades at a minibus carrying Iraqi army recruits to join the infantry at the Muthanna base, killing two men and wounding five other people, including a woman bystander, a police official said. The official, who declined be identified because he wasn't authorized to release the information, said the attack occurred on a heavily guarded road leading to the base.

The operation in Mosul is one of three recently launched by the U.S.-backed Iraqi government in a bid to clamp down on violence in the country. The other two have focused on Shiite extremists in the southern city of Basra and Baghdad's Sadr City district.

Despite continuing attacks, death tolls among Iraqi civilians and U.S. troops have dropped sharply in Iraq this month. An average of 17 Iraqis have been killed by violence each day this month, the lowest level since December 2005, according to an Associated Press tally.

At least 20 U.S. troop deaths have been recorded so far this month, putting May on track to be the lowest monthly toll this year, an AP count shows.

Al-Maliki touted his government's security and economic progress at a U.N. conference in Stockholm, Sweden.

"Iraq has achieved major success in the battle against terrorism with the support of the international community," he said.

Meanwhile, Iraq's Shiite vice president discussed security cooperation with Iranian officials during a previously unannounced visit to Iran, the government said Thursday.

Although both governments are dominated by Shiites, relations have been strained since al-Maliki launched a crackdown on Shiite militias and opened talks with the United States on a long-term security pact.

U.S. officials have frequently accused Iran of jeopardizing peace in Iraq by supplying weapons to anti-U.S. Shiite militias. Iran denies the allegation.

The visit by Vice President Adel Abdul-Mahdi, which took place during the last two days, was private, the government press office said.

Nevertheless, he met with Iranian President Mahmoud Ahmadinejad, newly elected parliament speaker Ali Larijani and top nuclear negotiator Saeed Jalili to discuss "security matters," the government statement said.

In a separate development, the British Embassy in Iraq, renewed appeals for the release of five Britons kidnapped in Baghdad a year ago Thursday.

The men — four security workers and a consultant — were seized during a visit to the Iraqi Finance Ministry by about 40 gunmen in police uniforms and driving official vehicles.

At the time, Iraqi officials blamed factions of the Mahdi Army, the feared militia of anti-U.S. Shiite cleric Muqtada al-Sadr, although the cleric's followers denied involvement.

In interviews Thursday with the British Broadcasting Corp., family and friends called for the release of the men. Only first names were used as stipulated by the British government for security reasons.

"A year is far too long for these men's families to be without them, and as fellow human beings, surely you can empathize with what their families are going through," said Caroline, who identified herself as the sister-in-law of a hostage named Alan. "So please, please, send them back."