BAGHDAD, Iraq — The Iraqi commander of the Baghdad security crackdown announced yesterday that Iraq will close its borders with Syria and Iran for 72 hours as part of the drive to end the violence that has threatened to divide the capital along sectarian lines.

Addressing the nation on behalf of Prime Minister al-Maliki, Lieutenant General Abboud Gambar also said Baghdad’s nighttime curfew would be expanded by an hour and permits allowing civilians to carry weapons in public would be suspended during all of the operation, which he suggested could last weeks.

General Gambar’s announcement came hours after a suicide truck bomber struck a government warehouse in a mainly Shiite neighborhood of the capital, killing at least 15 people and wounding 27, according to police and hospital officials. A parked car bomb also exploded near a bakery in another Shiite area, killing four people and wounding four, police said.

The general did not say when the borders would close, but another official said it was expected within two days. The official, who spoke on condition of anonymity because he was not authorized to speak to journalists, added that the borders would only partly reopen after the 72-hour closing.

America has long charged that Iran and Syria let extremists use their territory to slip into Iraq to attack American and Iraqi forces as well as civilians.

Iraqi authorities have routinely echoed the American charges against Syria, but they rarely make that claim regarding Iran, with which Iraq’s Shiite-led government has close relations.

General Gambar said Baghdad’s nighttime curfew would be extended by one hour when the security drive kicks off fully, running between 8 p.m. and 6 a.m.

The American military announced last week that the clampdown had already begun, although Iraqis have seen little evidence of that. President Bush has committed 21,500 more Americans to the operation, which is expected to involve a total of 90,000 Iraqi and American soldiers.

The campaign is widely seen as possibly the American military’s final attempt to calm the city. It will be the third attempt by American forces and their Iraqi allies to end violence in Baghdad since Mr. Maliki took office last May.

General Gambar said he would report to Mr. Maliki weekly to discuss progress in the operation.

His address suggested Iraqi authorities plan to exercise wide powers while waging the crackdown. A criminal court, for example, will hold emergency hearings on cases such as murder, theft, rape, kidnapping, damaging public property, and the possession and transfer of arms, he said.

General Gambar, a Shiite and a veteran of the 1991 Gulf War when he served in Saddam Hussein’s army, said security forces also plan to monitor mail, parcels, telegrams and wireless communication devices during the operation.

He said security forces would try to avoid intruding in places of worship, but he added that they would do so in “cases of extreme emergencies when it is feared that these places pose a threat to the lives of citizens or if they are used for unlawful purposes.” American and Iraqi authorities have often said Sunni insurgents use mosques to store arms or fire at troops.