TIKRIT, Iraq (AP) - U.S. fighter jets pounded suspected insurgent positions Tuesday in the largest bombardment of guerrillas in central Iraq since President Bush declared the end of major combat in May, the U.S. military said.

In northern Iraq, guerrillas detonated a roadside bomb, wounding two soldiers, the military said. On Monday, a U.S. civilian contractor was killed in an insurgent attack near Baghdad, the military said without elaborating.

The U.S. military has reacted forcefully to an upsurge in guerrilla activity in central and northern Iraq. On Monday, six insurgents were killed in gunbattles and 99 suspects were reportedly detained in a series of sweeps.

Near Baqouba, 30 miles northeast of Baghdad, U.S. jets and Apache helicopter gunships Tuesday blasted abandoned buildings, walls and trees along a road where attacks have been so common that troops nicknamed it "RPG Alley" after the rocket-propelled grenades used by insurgents. Fighter-bombers dropped 500-pound bombs and tanks fired their 120mm guns at suspected ambush sites, the military said.

On Monday, 4th Infantry Division soldiers also killed six alleged insurgents in the Tikrit area as they pressed their search for a former Saddam deputy, Izzat Ibrahim al-Douri, who is believed to be orchestrating attacks.

The attacks went on sporadically through the night, with sporadic explosions reverberating across Tikrit.

In fighting in central Iraq, U.S. soldiers destroyed 12 safe houses, 14 mortar firing positions and four ambush sites, said Lt. Col. William MacDonald, a military spokesman. No casualties were reported.

Elsewhere, an Iraqi militant group called Muhammad's Army claimed responsibility Monday for the Nov. 2 downing of a U.S. helicopter that killed 16 soldiers near Fallujah, west of Baghdad. The group warned that U.S. forces would face more attacks if they did not leave Iraq in 15 days. There was no way to independently verify the claims.

The group is seeking to return Saddam to power and consists of several hundred former Iraqi intelligence and security services. A group with this name is one of several that claimed responsibility for the Aug. 19 bombing of U.N. headquarters in Baghdad.

Despite the administration's efforts to repair infrastructure, Iraqis frequently complain about the slow pace of reconstruction seven months after the war that deposed Saddam's regime.

Coalition authorities have frequently pointed to the gradual restoration of electrical power as a benchmark of their success in rebuilding Iraq.

But those efforts suffered a major setback when the grid supplying the capital from power plants in the north collapsed Saturday.

U.S. administrators said the outages were a result of maintenance work on the national grid. But Iraqi government officials said they were caused by the collapse of steel pylons carrying high-tension lines after heavy rains and high winds.

Kareem Waheed, an undersecretary in the Electricity Ministry, said he was hopeful that power could be resupplied to Baghdad on Wednesday.

"We cannot cook, there is no water, and it is very cold without heating at night," said Leyla Najim, a librarian in central Baghdad. "The children cannot do their homework in the dark."

On Monday, the Italian Foreign Ministry confirmed the resignation of an Italian official of the U.S.-led coalition, who accused the occupation authorities of incompetence

State Department spokesman Richard Boucher, asked about the resignation, said the coalition authority has made "excellent progress" in several areas, including "the physical reconstruction of Iraq, the restoration of services to Iraqi people, the beginnings of political authority among the Iraqi ministers and now an accelerated path to political authority."

In Baghdad, shots were fired outside the Japanese Embassy about 3 a.m. Tuesday but no staffers were injured, the Japanese Foreign Ministry said in Tokyo.

More than one gunman was apparently involved, and they fled in a car after an Iraqi security guard at the embassy fired back, it said.

Japan was among the first countries to support the U.S.-led war against Iraq and is considering sending troops to help with reconstruction.

Meanwhile, a United Nations official was quoted Tuesday as saying the world body will continue to operate in Iraq through its local staff and quick visits by senior officials based in neighboring countries.

Ghassan Salameh, an adviser to Kofi Annan, told the Lebanese newspaper An-Nahar that a U.N. meeting in Cyprus last week came up with "temporary, work-around solutions" to cope with the absence of international staff after most of its employees were evacuated following the bombing of the U.N. office.

Some 4,000 local U.N. staff are still performing humanitarian work in Iraq, although the number is expected to drop to about 1,500 with the termination of the U.N.-run oil-for-food program at the end of November.