The Turkish military announced the operation on its Web site on Friday, but Prime Minister Recep Tayyip Erdogan later played down the mission, describing it as “limited” in size and emphasizing that the soldiers would return to Turkey “in the shortest possible time.”
Reports of the numbers of troops varied. According to Reuters, Turkey’s foreign minister and an unnamed American official in Baghdad said that that only a few hundred had been deployed, while Turkish television reported that the number was around 10,000.
In Baghdad, Rear Adm. Greg Smith, referring to the militants’ group, the Kurdistan Workers’ Party or P.K.K., described the attack as “an operation of limited duration to specifically target P.K.K. terrorists in that region.”
The militants want greater autonomy for Turkey’s Kurdish minority and have fought the Turkish military from hide-outs in both Turkey and Iraq for decades.
In Erbil, the northern Iraqi region’s capital, Kurdish leaders huddled in meetings with Kurdish military leaders and issued only brief statements to the press.
However, the tone of statements both from the Kurds and the Americans suggested that they were trying to tamp down nationalist sentiments and avoid inflammatory language.
The president of Kurdistan, Massoud Barzani, who often takes a bellicose tone, especially when talking about Turkey, was measured in his response and steered clear of threatening retribution. “We prefer that this would be solved politically,” he said.
“This trespasses on the Kurdistan Region’s sovereignty and on Iraq’s sovereignty,” Mr. Barzani said, but added, “We are not working to complicate the situation, but we will defend ourselves.”
Mr. Erdogan said he had called President Bush around midnight to tell him of the operation. The White House said Turkey had informed the United States beforehand.
“Turkey has given its assurances it will do everything possible to avoid collateral damage to innocent civilians or Kurdish infrastructure,” Admiral Smith said.
He added that the United States backed Turkey’s right to rout the terrorists who have used mountain camps across the Kurdistan border to stage attacks on Turkey.
“The United States continues to support Turkey’s right to defend itself from the terrorist activities of the P.K.K. and has encouraged Turkey to use all available means, to include diplomacy and close coordination with the Government of Iraq, to ultimately resolve this issue,” Adm. Smith said.
Tensions in the northern region started to rise on Thursday when Turkish tanks tried to leave two Turkish military outposts in northern Iraq, north of Dohuk and near Zakho. Turkey has long had outposts inside Iraq, where small numbers of special forces troops perform largely monitoring functions.
“The Kurdish Pesh Merga forces moved at once around 8 p.m. today and surrounded the Turkish camps and pointed guns toward the troops coming out of the camps, and that made the Turkish troops go back inside the camps again,” said Col. Hussein Tamuer, of the Kurdish border guard.
He added that there were no clashes but that the Kurdish Pesh Merga were “on full alert.”
Kurds are viewing the incursion as a “struggle between the Turks and the P.K.K.,” Colonel Tamuer said.
He added that if the attacks reached deep into Kurdish territory to where there were Kurdish civilians, it would be a “red line” and “the Pesh Merga will reply to their attacks.”
The conflict has been difficult for the United States because it sets Turkey, a NATO member and one of its closest allies in a troubled region, against the Iraqi Kurds, the most important American partners in the war in Iraq.
The Bush administration agreed to share information and to open airspace to the Turkish military last year, after attacks by the Kurdish group intensified. Turkey’s airstrikes against Kurdish targets, which began in December, were sanctioned by the United States.
Some American officials struck troubled tones. A deputy assistant secretary of state, Matthew J. Bryza, said the incursion was “not the greatest news,” Reuters reported from Brussels, while a Pentagon spokesman said the United States military had urged Turkey to bring the operation to a “swift conclusion,” the same news agency reported from Washington.
Even so, a flurry of recent visits by senior military commanders of both countries, including one this month in Washington by Gen. Ergin Saygun, Turkey’s deputy chief of the military, seem to indicate a relatively high level of mutual cooperation.
The operation is “more than a random hunt,” said Sedat Laciner, director of the International Strategic Research Organization, based in Ankara, the Turkish capital. It is “based on advanced technology, international cooperation and fine targeting.”
“It is much more sophisticated and professional than operations in the past,” said.
The military said the reason for the operation was to “prevent the region from being a permanent and safe base for the terrorists.”
The European Union’s foreign policy chief, Javier Solana, speaking in Slovenia, said, “We think this action is not the best response,” Reuters reported. “The territorial integrity of Iraq is for us very important.”
It was unclear whether the offensive would complicate relations between the United States and Iraqi Kurds, led by Jalal Talabani, Iraq’s president, and Massoud Barzani, the leader of the Kurdish north. But Iraq’s foreign minister, Hoshyar Zebari, also a Kurd, gave an early clue that the impact would be minimal, when he said, “There has not been any major incursion,” Reuters reported.
Turkish domestic politics were also in play. The military’s image was damaged in bruising political battles with Mr. Erdogan and his party last year, and a successful campaign against a common enemy could help repair it.
“Their success would ultimately help their image to get stronger,” Mr. Laciner said.
On Friday afternoon, the military air base in Turkey’s southeast town of Diyarbakir was buzzing with activity, said the state-run Anatolian News Agency, which reported that fighter jets and helicopters were taking off from the base to monitor the border.
Nearly 40,000 people have died in the fighting between the Turkish military and the P.K.K. over the past quarter century, though in recent years, death tolls have drastically diminished.
Turkey staged frequent incursions into northern Iraq before the American invasion. In 1992, as many as 70,000 Turkish troops crossed into Iraq, under an agreement with the country’s former ruler, Saddam Hussein.
But Turkey’s problems with its native Kurds — about a quarter of the country’s population — are impossible to solve through military means alone, and even former military officers have acknowledged the need for greater inclusion of the Kurds, who speak Kurdish instead of Turkish, into Turkish society. Mr. Erdogan said this month the government would add a Kurdish language channel to Turkey’s state television network.