KIRKUK, Iraq — The Turkish army sent soldiers about 1.5 miles into northern Iraq in an overnight operation today, Kurdish officials said. A Turkish official said the troops seeking Kurdish rebels were still in Iraq by midmorning.

Meanwhile, Secretary of State Rice made an unannounced visit to Kirkuk, the hub of Iraq’s northern oil fields.

The troops crossed into an area near the border with Iran, about 75 miles north of the city of Irbil, a spokesman for Kurdistan’s Peshmerga security forces, Jabar Yawar, said.

About 300 Turkish troops crossed the border at 3 a.m., a spokesman for the regional Kurdistan government, Jamal Abdullah, said. He said the region was a deserted mountainous frontier area.

The American Embassy in Baghdad declined to comment on reports of the Turkish operation.

The Kurdish Workers’ Party, or PKK, has battled for autonomy for southeastern Turkey for more than two decades and uses strongholds in northern Iraq for cross-border strikes.

It was not clear how long the Turkish soldiers who entered Iraq today would stay, but a Turkish government official said they were sent as “reinforcements” to existing Turkish troops stationed further inside Iraq.

“They are going there as reinforcements, they are not returning,” the official said on condition of anonymity as he was not authorized to speak to the media.

About 1,200 Turkish military monitors have operated in northern Iraq since 1996 with permission from local authorities. A tank battalion has been stationed at a former airport at the border town of Bamerni and a few other military outposts were scattered in the region. Ankara rotates the troops there.

Asked about a reported clash between the Turkish troops and Kurdish rebels inside Iraq, President Gul said: “From now on, whatever is necessary in the struggle against terrorism, it is being done.”

An Iraqi government spokesman, Ali al-Dabbagh, said the incursion “is not acceptable and will lead to complicated problems.”

“Iraq understands the threat the PKK represents, one that endangers Turkish security,” Mr. al-Dabbagh said. “But Iraq rejects any Turkish interference in Iraq.”

Mr. al-Dabbagh said the Iraqi government was given no warning about the incursion.

Mr. Abdullah, the spokesman for the regional Kurdish government, also criticized the operation and cautioned that Turkish forces should “be careful not to harm civilians” who might be living in the area.

“If the Turkish military conducts limited operations against the rebels, this is a problem of their concern,” he said. “But if this … leads to harm for civilians, we will absolutely be against that and reject that.”

On Sunday, Turkey conducted airstrikes against rebels from the Kurdish Workers’ Party, or PKK, in northern Iraq. As many as 50 fighter jets were involved in the attack, the biggest against the PKK in years.

An Iraqi official said the planes attacked several villages, killing one woman. The rebels said two civilians and five rebels died.

The Iraqi parliament yesterday condemned the bombing, calling it an “outrageous” violation of Iraq’s sovereignty. Turkey said Sunday’s attack used American intelligence and was carried out with tacit American approval.

Washington is trying to balance support for two key allies: the Turkish government and the Iraqi Kurds. Despite their apparent support for a limited raid, America remains firmly opposed to any major Turkish military operation into northern Iraq — which could disrupt one of the calmest areas of Iraq and run the risk of destabilizing the entire region.