BAGHDAD, Iraq (AP) – It was just past sunset when a car carrying an Iranian diplomat was cruising through the streets of a leafy Shiite neighborhood. Suddenly, two cars filled with uniformed men blocked the way, forced him into a vehicle and sped off.

Jalal Sharafi’s abduction Sunday evening threatens to escalate the tense standoff between Iran and the United States – and could swell into a major diplomatic crisis for Iraq’s fragile, Shiite-dominated government.

Iran has blamed America for the kidnapping – or possibly arrest – of Mr. Sharafi, a second secretary at the Iranian Embassy. Tehran said it holds the Americans responsible for his safety.

Ameircan authorities deny any role in the disappearance. “We don’t really know a whole lot about it at this point,” White House spokesman Tony Snow said. “We know that the Iraqi government is investigating.”

Publicly, the Iraqi government is saying as little as possible.

Suspicion also has fallen on a range of possible culprits – Iraqi commandos, rogue elements in the security forces, Sunni insurgents or criminals seeking a big ransom.

Some Shiite lawmakers said the abduction was staged by an Iraqi commando unit that reports directly to the American command – an allegation strongly denied by an American.spokesman.

Details of the kidnapping remain murky, but one government official said it began when gunmen wearing Iraqi army uniforms blocked Sharafi’s car in the Karradah district, forced him into one of their two vehicles and sped away.

Iraqi police then opened fire, disabling the second vehicle and arresting the four gunmen inside, the official said.

Police took the four to a police station. The next day, Iraqis in uniform appeared there, showed government badges and demanded the four suspects – ostensibly to transfer them to another lockup, the official said.

The authorities complied, and the men disappeared. Spokesmen of both the Interior Ministry and the Defense Ministry, which together control Iraqi security forces, said they had no information and no idea where the suspects went.

Shiite lawmakers said they believed Mr. Sharafi was detained in an intelligence operation carried out by the Iraqi Special Operations Command, an elite unit under the direct supervision of the American military.

The lawmakers and officials spoke on condition of anonymity because they were not authorized to release the information.

But American. military spokesman Lieutenant Colonel. Christopher Garver said no American or coalition troops were involved in the abduction. “We’ve checked with our units and it was not an MNF-I (Multi-National Forces – Iraq) unit that participated in that event,” he said.

Colonel Garver said he was also ruling out involvement by any Iraqi unit that reports directly to the American command – which would include Special Operations troops.

Those denials did little to soothe Iran’s anger.

Iran’s Foreign Ministry said it had summoned the Swiss and Iraqi ambassadors to Tehran to protest the abduction of the diplomat. Switzerland looks after American interests in Iran since Tehran and Washington have no diplomatic relations.

Ministry spokesman Mohammad Ali Hosseini said Iran “strongly condemns this aggressive act, which is in violation of international law” protecting accredited diplomats.

“Iran holds American forces in Iraq responsible for the safety and life of the Iranian diplomat,” he told Iran’s official Islamic Republic News Agency.

Karradah is an unlikely venue for an assault on an Iranian diplomat. The heavily Shiite neighborhood is controlled by the Supreme Council for the Islamic Revolution in Iraq, or SCIRI, a major Shiite party with close ties to Iran.

SCIRI was founded in Iran in 1982 by Iraqi Shiite militants who fled Saddam Hussein’s Sunni-dominated regime. Iran’s Revolutionary Guards organized and trained SCIRI’s armed wing, the Badr Brigade, which fought alongside Iranian soldiers in the 1980-1988 Iran-Iraq war.

The abduction occurred as tension between Iran and the United States is mounting over alleged Iranian support of Shiite extremists in Iraq and U.S. efforts to force Tehran to abandon its suspected nuclear weapons program. Iran says it wants to use the technology to generate nuclear power.

The incident came nearly a month after U.S. detained five Iranians in northern Iraq and accused them of having links to the Al-Quds Brigade – a part of the Iranian Revolutionary Guards which trains and finances armed Shiite groups outside Iran.

Two Iranian diplomats also were detained in a Dec. 21 roundup of a group of 10 suspects. The diplomats were interrogated and released to Iranian officials eight days later.

The White House has authorized American troops in Iraq to kill or capture Iranian agents deemed to be a threat, saying evidence is mounting that Iran is supporting terrorists inside Iraq and is a major supplier of bombs and other weapons used to target U.S. forces. Tehran has denied it.

American officials believe Iranian agents may have been behind the Jan. 20 attack in the southern city of Karbala in which four American soldiers were kidnapped and slain. A fifth American was killed in the firefight.

Those suspicions are based in part on the skill and cunning of the attack – in which gunmen more American-style uniforms, drove to the scene in American vehicles and apparently used American weapons.

Meanwhile, American and Iraqi officials said American authorities are investigating allegations that an Iraqi Shiite lawmaker took part in the 1983 bombing of the American and French embassies in Kuwait and is a conduit for Iranian weapons and supplies smuggled to Shiite militias.

Jamal Jaafar Mohammed, who was elected to parliament in December 2005 on the Shiite ticket, was sentenced to death in Kuwait years ago for his role in the bombings, in which five people were killed and 86 wounded, but fled to Iran, CNN reported. CNN said U.S. military intelligence in Iraq believes Mohammed helps Iranian special forces in Iraq as “a conduit for weapons and political influence.”

Mr. Mohammed returned to Iraq after the fall of Saddam, but has not attended any legislative sessions since last year and is believed to be in Iran, Shiite lawmakers said.

In Iraq, however, there is no shortage of groups capable of a kidnapping – and no shortage of speculation with every spectacular bombing, mass abduction or suicide attack.

Kidnappings by gunmen wearing uniforms and traveling in government vehicles have occurred with alarming frequency in Baghdad over the past two years. Last July, gunmen wearing police uniforms seized the head of Iraq’s Olympic committee and dozens of others during a meeting in Karradah.

Most of them are still missing, including the committee president, Ahmed al-Hijiya.

Such kidnappings have been variously blamed on rogue elements within the Shiite-controlled police, Shiite militias, Sunni insurgents and criminal gangs, and intelligence units that detain people secretly to avoid Iraqi laws limiting the amount of time a suspect can be held without charge.

American and coalition forces are holding thousands of people without charge as security risks, citing the U.N. resolution under which the Americans and their international partners operate here. The resolution does not grant Iraqi forces the same authority.

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AP writer Ali Akbar Dareini in Tehran, Iran, and Qassim Abdul-Zahra in Baghdad contributed to this report.