BAGHDAD, Iraq - Iraq will seal its borders, extend a curfew and restrict movement to protect voters during the Jan. 30 election, officials announced today after the latest major insurgent attack - a suicide bombing that killed three people outside the offices of a leading Shiite political party.

Amid the insurgent campaign to ruin Iraq's election, a Catholic archbishop kidnapped by gunmen in the northern city of Mosul was released today, a day after his abduction. The Vatican had called his abduction a "terrorist act."

A video surfaced today showing eight Chinese construction workers held hostage by gunmen claiming the men are employed by a company working with U.S. troops, in the latest abduction of foreigners in Iraq. China's official Xinhua News Agency said diplomats were "making all efforts to rescue" the hostages.

The men from China's southern Fujian province went missing last week while traveling to Jordan, Xinhua said.

Today's suicide car bombing in Baghdad gouged a crater in the pavement, left several vehicles in flames and spread shredded debris on the street outside the offices of the Supreme Council for the Islamic Revolution in Iraq, a main contender in the election. The Shiite party, known as SCIRI, has close ties to Iran and is strongly opposed by Sunni Muslim militants.

The assailant told guards at a checkpoint leading to the party's office that he was part of SCIRI's security staff, and he detonated his bomb-laden car at the guard post when he was not allowed to enter.

The U.S. military reported four dead, including the bomber, and four injured.

"SCIRI will not be frightened by such an act," party spokesman Ridha Jawad said. "SCIRI will continue the march toward building Iraq, establishing justice and holding the elections."

Sunni Muslim militants, who make up the bulk of Iraq's insurgency, are increasingly honing in on Shiites in their effort to ruin the election that is widely expected to propel their religious rivals to a position of dominance. Many Sunnis argue that security is precarious and the election should not take place under foreign occupation.

In another attack apparently designed to scare Shiites away from the polls, masked gunmen killed a Shiite Muslim candidate in Baghdad.

The Independent Electoral Commission announced that the country's international borders would be closed from Jan. 29 until Jan. 31, except for Muslim pilgrims returning from the hajj in Saudi Arabia.

Iraqis also will be barred from traveling between provinces and a nighttime curfew will be imposed during the same period, according to a statement from the commission's Farid Ayar.

Such measures had been expected because of the grave security threat. U.S. and Iraqi authorities are hoping to encourage a substantial turnout but fear that if most Sunnis stay away from the polls, the legitimacy of the new government will be in doubt.

The interior minister warned that if the country's Sunni Arab minority bows to rebel threats and stays away from the polls, the nation could descend into civil war.

Falah Hassan al-Naqib, a Sunni, told reporters he expects Sunni insurgents to escalate attacks before the election, especially in the Baghdad area. Voters are to choose a new 275-member National Assembly.

"If any group does not participate in the elections, it will constitute treason," al-Naqib said, adding that "boycotting the elections will not produce a National Assembly that represents the Iraqi people" but will cause "a civil war that will divide the country."