Turkey sent soldiers, bomber planes and helicopter gunships into Iraq on Wednesday, reports the Associated Press.
Authorities have not confirmed the operation, but local media reports say that Turkish troops have gone roughly 2.5 miles across the border.
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Both airstrikes and ground troops were deployed early on Wednesday morning in the Qandil mountains in northern Iraq, according to Al Jazeera.
Soldiers have already killed 15 Kurdish rebels in clashes on the Turkish side of the border, reports Reuters, citing security sources.
They were responding to simultaneous attacks on police and army posts, carried out overnight in several locations in the predominantly Kurdish province of Hakkari in south-east Turkey.
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Kurdish separatist group PKK, the Kurdistan Workers' Party, was responsible for the attacks, according to a Turkish security source.
At least 26 soldiers died in the attacks, making them the deadliest on the Turkish military in almost 20 years, the BBC reports.
The governments of Turkey and Iraq have an agreement that allows the Turkish military to make "hot-pursuit" operations into Iraq, says Al Jazeera.
Turkish President Abdullah Gul pledged that Turkey would make the firmest possible response:
"No one should forget that those who make us suffer this pain will be made to suffer even stronger. They will see that the vengeance for these attacks will be immense."
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