Truckloads of weary and unshaven Turkish troops returned Friday from Iraq as Turkey ended an eight-day cross-border offensive against Kurdish rebels, meeting U.S. demands for a quick campaign.

Washington and Baghdad welcomed the move, but Turkey warned that the forces would return if necessary.

A key test of the effectiveness of Turkey's ground incursion could come in the weeks ahead with the arrival of spring, the traditional start of the fighting season of the rebel Kurdistan Workers' Party, or PKK. In the past, guerrillas have taken advantage of the melting snows and infiltrated Turkey from bases in Iraq, and any surge in PKK attacks could trigger another tough response from the Turkish military.

"It is very clear that an established group like the PKK will not be eliminated with one or two more cross-border operations. Turkey needs pinpoint operations against the group's leadership, like Israel's operations against Palestinian groups," said Sinan Ogan, head of the Turkish Center for International Relations and Strategic Analysis in Ankara.

Moreover, the discrimination and poverty that triggered the Kurdish insurgency in Turkey in 1984 persist, although the government has taken steps in recent years to ease restrictions on Kurds as part of its bid to join the European Union. The PKK's power has dwindled since its 1990s heyday, and Europe and the United States consider it a terrorist group, but it still enjoys support in the country's predominantly Kurdish southeast and some urban centers.

The PKK has tempered its demands over the years, initially calling for an independent state and later for autonomy in the southeast and cultural rights. The conflict has killed up to 40,000 people.

Turkey's first major incursion into Iraq for about a decade reflected the sensitive nature of its alliance with the United States, which provided intelligence to the Turkish military but sought a short campaign to preserve the relative calm of the mostly Kurdish region of northern Iraq. The troop withdrawal came a day after President Bush and Defense Secretary Robert Gates told Turkish leaders they should end the offensive as soon as possible.

"Any influence, either foreign or domestic, on this decision by the Turkish Armed Forces is out of the question," the Turkish military said. "Terrorist activities in Iraq's north will be observed in the future and no threat against Turkey from this region will be allowed."

Gen. Yasar Buyukanit, the military chief, said it was "pure coincidence" that the withdrawal was announced one day after Gates issued his appeal during a visit to Ankara, Dogan news agency reported.

"This decision was made because the operation had reached its targets," Buyukanit said. "When the U.S. defense secretary stepped into Turkey, the withdrawal had been partly realized."

CNN-Turk television quoted Prime Minister Recep Tayyip Erdogan as saying: "Everything has been realized according to the plan. No civilian has been harmed in the operation."

Firat, a pro-Kurdish news agency, quoted PKK officials as saying the Turkish withdrawal was made under pressure from Kurdish militants and that it amounted to a victory for the rebels. Senior rebel commander Murat Karayilan congratulated his fighters, the agency said.

Turkey, which barred U.S. troops from using its soil as a springboard to invade Saddam Hussein's Iraq in 2003, had expressed frustration with Washington and the U.S.-backed Iraqi government for their perceived failure to crack down on the PKK.

In Washington, National Security Council spokesman Gordon Johndroe said Turkey's incursion "was a targeted and relatively short operation."

"But I would certainly expect that in the future, that unless the PKK gives up terrorism, that we're going to have to continue to work with the Turks and the Iraqis to go after them," Johndroe said.

Iraqi authorities had said they do not support the PKK but objected to Turkey's military action. Iraqi President Jalal Talabani, himself a Kurd, welcomed the end of the incursion.

"This withdrawal indicates the credibility of the Turkish government's statements that the military operation is limited and temporary," his office said in a statement.

Iraqi Foreign Minister Hoshyar Zebari, also a Kurd, credited the U.S. with playing an "instrumental" role in pressing Turkey to leave.

The Turkish military said the operation targeted 300 rebels in Iraq's Zap region, and 240 of them were killed. Turkish losses stood at 27. The PKK has disputed Turkey's estimate of slain rebels, and independent confirmation of the toll in the remote area is virtually impossible. Turkey has previously said there were up to 3,800 PKK militants in northern Iraq, and as many as 1,500 inside Turkey.

"Without a doubt, it is impossible to render the entire terrorist organization ineffective with an operation in only one region. However, it is shown to the group that Iraq's north is not a safe area for terrorists," the military said.

The military said commando units, airborne troops, tanks and armored personnel carriers were used in the operation, and F-16 warplanes and long-range artillery pounded suspected rebel positions. It said troops, trained for winter warfare, took the PKK by surprise. However, there had been reports prior to the incursion that many PKK rebels had dispersed, fearful of an attack.

Soldiers in trucks driving through the border town of Cukurca and into Turkey's interior on Friday gave thumbs-up signs. Some had camouflage paint on their faces, wore snow boots and woolen caps, and held machine guns.

Despite Turkey's avowal that its only target was the PKK, one analyst speculated that Turkey also delivered a warning to Iraqi Kurds who run a virtual mini-state in northern Iraq. Turkish officials fear their separatist aspirations could inflame similar sentiment among Turkish Kurds, who only recently were awarded limited cultural rights such as Kurdish-language courses and television broadcasts.

"They made a point — they can do what they want in that region," Aliza Marcus, author of "Blood and Belief: the PKK and the Kurdish Fight for Independence," said of Turkey's leadership. "The message to Iraqi Kurds is: 'Be careful. We are here."'