TAL AFAR, Iraq – U.S. and Iraqi troops swept into the insurgent stronghold of Tal Afar early Saturday, conducting house-to-house searches and battering down walls with armored vehicles in a second bid to clean the city of militant fighters.

Some 30 miles south of Baghdad, meanwhile, police found the bodies of 18 men who had been handcuffed and shot to death in Iskandariya, a town where dozens of killings have been reported in escalating vengeance killings by Shiite Muslim and Sunni Aram “death squads.”

“Two days ago gunmen in police uniforms broke into their houses in a Shiite neighborhood of Iskandariya,” police Capt. Adel Kitab said of the latest victims.

In the capital, Baghdad International Airport reopened early Saturday after a day’s closure in a payment dispute between the government and a British security company. Global Strategies Group said it agreed to resume security work after the government promised to pay half of what the company said it is owed.

Iraq police said two mortar shells were fired into the Green Zone that houses the U.S. Embassy, the Iraqi parliament and government offices. There was no word on casualties or damage.

In the Tal Afar offensive, which had been expected for weeks, coalition forces faced several hundred lightly armed insurgents in the largely deserted city, 260 miles northwest of Baghdad and about 60 miles east of the Syrian border.

There was heavy gunfire in the Sarai district, the oldest part of the city and the major insurgent stronghold.

“I can see why the terrorists chose this place for a fight, it’s like a big funnel of death,” Sgt. William Haslett of Rocklin, Calif., said of the twisting streets and alleys in the old city.

Prime Minister Ibrahim al-Jaafari announced the 2 a.m. start of the offensive in a statement issued early Saturday. At a news conference later, he said the insurgents had been trying “to isolate Tal Afar from the political process as we are preparing for the referendum on the draft constitution.”

Tal Afar residents were largely Turkomen, with ethnic and cultural ties to Turkey to the north. They are mostly Sunni Muslims but had been governed since the ouster of

Saddam Hussein by a U.S.-backed Shiite Muslim city government and police force.

Interior Minister Bayan Jabr said 48 insurgents had been captured so far, along with mortars and communications gear. He said Iraqi troops had suffered two wounded and no deaths.

Defense Minister Saadoun al-Dulaimi said that in the past two days, 141 “terrorists” had been killed and 197 wounded. Five government soldiers died and three were injured, he said.

Al-Dulaimi said 11 Iraqi army battalions and three battalions of paramilitary police were engaged in the offensive, along with three battalions of U.S. troops, and promised Iraqi forces would broaden the offensive against insurgents north and west of Baghdad, right up to the Syrian border.

“We say to our people in (the insurgent strongholds of) Qaim, Rawa, Samarra and Ramadi, we are coming and terrorists and criminals will not be able to hide there,” he said.

He complained that neighboring nations had not done enough to stop the flow of foreign fighters.

“I regret to say that instead of sending medicines to us, our Arab brothers are sending terrorists,” al-Dulaimi said.

U.S. forces cleared Tal Afar of militants last year but quickly withdrew, leaving behind a force of only 500 that was unable to block the militants’ return.

In a bid to soften resistance, the U.S. military carried out repeated air and artillery strikes on targets in the city, where most of the population of 200,000 was reported to have fled to the surrounding countryside.

On Friday, the government issued a statement hinting a major attack was imminent, and the U.S. military reported killing 11 insurgents during raids over the past two days. The Iraqi military claimed it had arrested 150 foreign fighters who had infiltrated from

Syria.

In Baghdad, acting Transportation Minister Esmat Amer told The Associated Press that the city’s main airport — Iraq’s only reliable and relatively safe link to the outside world — reopened after negotiations overnight between the government and the British company.

“We have reached agreement with the Global security firm, and the airport is open now for domestic and international flights,” said Amer.

Company spokesman Giles Morgan told AP from London that Global agreed to return to work after the government promised to pay 50 percent of what was owed. Morgan said the company and the government were continuing talks on a future contract.

Amer confirmed the 50 percent agreement.

The company has provided security at the airport 12 miles from central Baghdad since last year. On Friday, Global suspended operations, claiming the transportation ministry was six months behind in payments.

Under a deal negotiated with the defunct U.S.-led Coalition Provisional Authority, Global was paid $4.5 million a month for airport security. The interim Iraqi government sought unsuccessfully to reduce that charge after it took over from the CPA last year.