(Recasts with casualties in paragraph 6)
ANKARA, Feb 22 (Reuters) - Thousands of Turkish troops have crossed into northern Iraq to hunt Kurdish rebels, television and a military source said on Friday, escalating a conflict that could undermine stability in the region.
Turkey's military said the cross-border offensive, possibly the largest in a decade, would continue until they had stopped the threat from PKK rebels, who have been using northern Iraq as a base to stage attacks in Turkey.
It said in a statement 24 PKK rebels and five soldiers were killed in clashes in Iraq. It also said at least 20 rebels were killed in separate aerial attacks.
The United States urged Turkey, a key regional ally, to limit its offensive to precise PKK targets and to bring the operation to a swift conclusion. Iraq's government called on Turkey to respect its sovereignty and to avoid any military action which would threaten security.
The European Union and the United Nations also urged restraint, fearing the offensive could jeopardise the most stable region in Iraq at a time when security is improving, and also rekindle tensions between Turks and ethnic Kurds.
The Turkish military said its troops had entered Iraq late on Thursday to destroy PKK camps and hunt rebels of the Kurdistan Workers Party (PKK), which has been battling for decades to create a Kurdish homeland in southeast Turkey.
"The operations inside Iraq will intensify tomorrow," said a Turkish military source, who declined to be named.
Turkish television said between 3,000 and 10,000 soldiers had entered Iraq, but several Iraqi officials and a military source with U.S.-led coalition forces in Baghdad said only a few hundred troops were involved.
The senior Turkish military source said two brigades made up of around 8,000 troops had taken part in the offensive.
"The Turkish Armed Forces, which attach great importance to Iraq's territorial integrity and stability, will return home in the shortest time possible after its goals have been achieved," the Turkish General Staff said in a statement.
It did give the size or length of the surprise operation, given the poor weather conditions.
Turkey's government and military have come under domestic pressure to crush the PKK after a series of deadly attacks on their troops late last year.
Ankara blames the PKK for the deaths of nearly 40,000 people since it began its armed struggle in 1984. Washington and the EU, like Turkey, classify the PKK as a terrorist organisation.
Turkey says it has the right under international law to hit the PKK in Iraq. Turkey says some 3,000 rebels are based there.
Turkey's military has been bombing PKK positions in northern Iraq since securing parliament's authorisation to carry out cross-border operations in October.
"I sincerely believe that this operation will contribute to Iraq's stability and peace in the region," Turkish President Abdullah Gul said in a statement on Friday.
Turkey appeared to be seeking to deal the PKK a crushing blow before weather conditions improve and rebels are more easily able to cross the mountains back into Turkish territory.
The Iraqi Red Crescent (IRC) said four bridges had been destroyed and 11 families, fewer than 100 people, had been displaced from two villages about 1-2 km (0.6-1.2 miles) inside the border.
"The civilians are scared because they don't know how far the Turkish army is going to enter into Iraq," IRC President Said Hakki told Reuters.
The central Baghdad government, which has little sway over mainly Kurdish northern Iraq, has repeatedly called for a diplomatic solution to the PKK presence.
Referring to what he said were Turkish forces targeting a number of bridges, Iraqi Foreign Minister Hoshiyar Zebari told Al Arabiya television: "... it is not Turkey's right to create instability and hit targets other than the PKK. This is what makes the situation dangerous ... and we fear military errors that may have harmful consequences for all sides."
Turkey launched several major land offensives in the 1990s into northern Iraq against the separatist movement and has since kept small contingents of troops at several bases there.
"Militarily, even 50,000 troops in the 1990s were not able to destroy the PKK, but psychologically this operation could be quite effective. It has taken the PKK by surprise," said Gareth Jenkins, an Istanbul-based expert on Turkish security issues. (Additional reporting by Michael Holden and Mariam Karouny in Baghdad, Matt Spetalnick in Washington, Gareth Jones and Selcuk Gokoluk in Ankara, Firouz Sederat in Dubai; Editing by Stephen Weeks)
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