Hundreds of Turkish soldiers crossed into northern Iraq on Wednesday pursuing Kurdish guerrillas who stage attacks on Turkey from hideouts there, Turkish security officials and an Iraqi Kurd official said. The reports came amid worries Turkey might launch an offensive against the rebel bases, touching off a conflict with US-backed Iraqi Kurds in one of Iraq's most stable regions. The U.S. is urging its NATO ally not to strike, and Turkey's foreign minister denied any incursion occurred. An American intelligence official in Washington, who agreed to discuss the tense situation along the frontier only if not quoted by name, said the reports of a border crossing should be treated with skepticism. The official said some Turkish officials might be feeling pressure to show increasingly angry Turks that the government is responding to a recent escalation of attacks by PKK rebels, who are fighting for autonomy in Turkey's heavily Kurdish southeast. On Monday, for instance, Kurdish rebels assaulted a Turkish outpost and killed seven soldiers. Three Turkish security officials said troops crossed the border Wednesday. But they described the operation as just a "hot pursuit" raid that was limited in scope, and one said the soldiers left Iraqi territory by the end of the day. The officials, all based in southeastern Turkey, spoke on condition of anonymity because they were not authorized to speak to journalists. Turkish authorities rarely acknowledge such military operations against the PKK, but the army has conducted brief raids across the border in the past. Despite the dispute over whether an incursion happened, the reports were likely to heighten anxieties over whether Turkey is planning a large-scale invasion. The last such operation was in 1997 and involved 50,000 soldiers. Turkish leaders have said they are considering an offensive, and have sent more troops and equipment to the frontier. But they hope the US and Iraqi Kurds will stage their own crackdown on the separatists, who raid southeast Turkey after resting, training and resupplying in Iraq. Washington lists the PKK as a terror group, but most U.S. troops in Iraq are busy dealing with violence elsewhere and most of the 16,500 U.S. soldiers in the north are engaged in training Iraqi forces. The Iraqi Kurd administration, meanwhile, has testy relations with Turkey, which has accused it of backing the PKK movement. One Turkish security official said 600 commandos entered Iraq before dawn after Kurdish rebels shot at Turkish patrols near the Turkish border town of Cukurca. The commandos returned to Turkey later in the day, the official said. Two other officials said troops went less than two miles into a remote, mountainous area in Iraq. An Iraqi Kurd security official in the Shanzinan area said 150 Turkish soldiers occupied a mountain about a half mile inside Iraq for an hour and then left. The official, speaking on condition of anonymity, said 200 other Turks staged a similar cross-border operation around the same time in the nearby Sirzeri area. It was not immediately clear whether the Kurdish official referred to the same raid cited by the three Turkish officials. Turkey's private NTV television quoted Foreign Minister Abdullah Gul as saying the reports of a cross-border operation were false. "There is no such thing, no entry to another country. If such a thing happens, then we would announce it," Gul said. "We are in a war with terror. We will do whatever is necessary to fight terrorism." Several officials at the Pentagon said they had seen nothing to confirm a border crossing by Turkish troops. But one said small numbers of Turkish soldiers occasionally conduct counterinsurgency operations inside Iraq. The officials insisted on speaking anonymously. The White House also said there had been "no new activity" in northern Iraq. But Gordon Johndroe, a spokesman for the National Security Council, repeated that Washington remains "concerned about the PKK and the use of Iraq as a safe haven."