BAGHDAD, Iraq – Terrorists kidnapped an American, a Nepalese, and four Iraqi guards in a bloody assault on their office in the capital yesterday, and gunmen assassinated Baghdad’s deputy governor in a drive-by shooting, new violence that came as voter registration began for vital January elections.

West of the capital, American troops clashed with Sunni insurgents, and American artillery pounded suspected terrorist positions in Fallujah, witnesses said.

American forces are gearing up for a major offensive against Fallujah, the strongest bastion of Sunni insurgents. The order to launch what would likely be a bloody assault must come from Prime Minister Allawi, who warned Sunday that his patience with negotiations was thinning.

American and Iraqi officials hope to curb the insurgency in time for national elections by the end of January.

A handful of Iraqis showed up for the first day of voter registration in central Baghdad yesterday. They refused to allow TV cameras to film them for fear of future retaliation.

To help protect the voting, fresh American soldiers arrived in the capital yesterday – reinforcements that push the total American military presence in Iraq to around 142,000, the highest level since the summer of 2003.

The latest in Iraq’s wave of kidnappings came when gunmen stormed the offices of a Saudi company in the upscale Mansour district of Baghdad, sparking a battle with guards during the evening iftar meal when Muslims break their daylong fast in the holy month of Ramadan, police said.

One attacker and one guard were killed in the fight, before the gunmen made off with their captives, police said. Police Lieutenant Colonel Maan Khalaf identified the captives as an American, a Nepalese, and the four Iraqis. American Embassy spokesman Bob Callahan confirmed that one of the victims was American.

“We heard gunfire. I went outside to see what’s going on when a man pointed a machine gun at me and said: ‘Get in or else I’ll shoot at you,’ ” said a man who lives in the neighborhood, Haidar Karar.

From his house he saw “at least 20 attackers, some masked and some not.” He said some were wearing traditional Arab robes and all were carrying automatic weapons.

The office is about 500 yards from a residence from which residents kidnapped two Americans and a Briton in September. All three were later beheaded. An Al Qaeda-linked group led by Jordanian terrorist Abu Musab al-Zarqawi claimed responsibility for the slayings.

Twelve Americans have been kidnapped or are missing in Iraq, and at least three of them have been killed, including an American slain by Mr. al-Zarqawi’s followers in April. The group also claimed responsibility for the abduction of a Japanese hostage whose decapitated body was found on Saturday, wrapped in an American flag and dumped on a Baghdad street.

Also yesterday, gunmen opened fire on a car carrying Baghdad province’s deputy governor, Hatim Kamil, to work yesterday, killing Kamil, said the Baghdad governor, Ali al-Haidari. Two of Kamil’s bodyguards were wounded, Interior Ministry spokesman Colonel Adnan Abdul-Rahman said.

A known terrorist group, the Ansar al-Sunnah Army, claimed responsibility for the attack in southeastern Baghdad.

“This is the fate of whoever is aiding or supporting the crusaders against the Muslims and mujahedeen,” the group said on its Web site. It was impossible to verify the claim’s authenticity.

Terrorists have killed dozens of Iraqi politicians and government workers in recent months in a bid to destabilize the country’s reconstruction.

The group also said it was behind the assassination of the deputy governor of Diyala province on Friday in the central Iraqi city of Baqouba. Aqil Hamid al-Adili, an assistant to the governor, was killed by unidentified gunmen as he was sitting in a friend’s office.

Mr. Allawi’s speech Sunday seemed aimed at preparing the Iraqi public for an onslaught in Fallujah, Mr. Allawi warned of civilian casualties, saying that if he orders an assault, it would be with a “heavy heart.”

“But I owe, owe it to the Iraqi people to defend them from the violence and the terrorists and insurgents,” he said. Commanders have estimated that up to 5,000 Islamic terrorists, Saddam Hussein loyalists, and common criminals are holed up in Fallujah.

He did not give a deadline for how long he would give negotiations with Fallujah’s city leaders in which he demands the handover of foreign fighters.

In a position that appeared to contrast with Mr. Allawi’s, the country’s interim president said a military assault was the wrong solution, according to an interview published yesterday.

President al-Yawer, a Sunni Muslim, told the Kuwaiti daily Al-Qabas that dialogue must continue and that terrorists “want nothing but a military solution, and the continuation of bleeding among Iraqis.”