Updated

The U.S. military's northern front against Iraq appears to be building, with American planes landing in the Kurdish north and more airstrikes pounding positions of a militant Islamic group with alleged Al Qaeda and Baghdad ties.

Four U.S. planes carrying "scores" of American military personnel landed at the Bakrajo airstrip, 10 miles west of Sulaymaniyah, late Saturday, a high-level Kurdish official said on condition of anonymity. They joined Special Operations troops already in the region.

Additional U.S. aerial attacks began Friday night and, a day later, targeted suspected positions of the militant Ansar al-Islam group, military officials said.

There were no details about casualties. The Friday night assault left scores dead, mostly members of another Islamist group accused of supporting Ansar, military officials said.

The Kurds have already amassed troops in the autonomous region they control near the border with Turkey, awaiting a decision on whether they will attack Saddam Hussein's forces.

The Kurds are also keeping a close on eye on Ansar al-Islam, which is suspected of links to Al Qaeda and which has been attacking Kurdish fighters sporadically over the past year. The Kurds fear Ansar could step up its activities if the a large American force moves in.

At the U.S. Central Command in Qatar, Lt. Gen. John Abizaid confirmed that the United States was "reinforcing our presence" in the north but gave no details.

The Kurdish official said more U.S. planes and personnel were scheduled to arrive in coming days and already may have landed at other airstrips in the Kurdish autonomous area, which has been under American and British aerial protection since the 1991 Gulf War.

The American planes originally were scheduled to land two months ago, but were delayed as Americans attempted to sort out a military strategy, the official said.

Ansar strongholds -- as well as the Baghdad-controlled strategic oil cities of Kirkuk and Mosul -- are possible U.S. targets, the official said. On Sunday, numerous bursts of anti-aircraft artillery were heard from the direction of Mosul.

The United States wanted to use Turkey to attack Iraq from the north, but the Turkish parliament refused to grant access to Turkish bases after weeks of wrangling over financial compensation and arrangements for sending Turkish troops into northern Iraq.

Turkish Prime Minister Recep Tayyip Erdogan said Sunday his government was seeking to send troops into northern Iraq to prevent instability at the Turkish-Iraqi border.

Erdogan said in a televised address that he wanted to send soldiers into northern Iraq to quell any Kurdish rebellion and to prevent an influx of Iraqi refugees. He said Ankara and Washington had "reached agreement" on preventing a breakup of Iraq, but did not say whether that understanding included sending in Turkish troops.

Turkey fears the Kurds, as Saddam's regime is overthrown, will seize the northern oil fields or establish an independent state, thus complicating Turkey's conflict with its own Kurdish minority. American officials fear clashes between Turkish forces and Iraqi Kurds.

On Friday, Turkey said U.S. warplanes could fly through Turkish airspace on their way to Iraq.

Barham Salih, prime minister of the Patriotic Union of Kurdistan government controlling the eastern half of the autonomous Kurdish enclave, declined to confirm the landing of U.S. forces. But he said such an incursion would be received warmly by the mostly pro-American Kurds.

"Americans are liberators," he said. "They are welcome in Iraq and they are welcome in Kurdistan. They are welcome to come here and help bring us freedom."

The Arab television station Al-Jazeera, reporting from Sulaymaniyah, quoted witnesses as saying U.S. airborne troops landed by helicopter at a base near the city.

The Kurdish official said the planes landed in darkness, using no lights, and departed when the personnel left. Residents living near Bakrajo airstrip described loud, strange noises late Saturday night, and four buses leaving the area.

Small groups of American forces have scoured the countryside for months, and the Kurds long have awaited more.

Mohammad Haji Mahmoud, leader of the Kurdistan Social Democratic Party and a key member of the Iraqi opposition, said the Americans are welcome to use Kurdistan as a staging ground for a northern assault against Saddam's regime.

"We're not going to say no to anything the Americans want," he said. "America is the true liberator and the only one who could liberate us from this regime. We couldn't do it with our rusty Kalashnikovs in more than 40 years."