Turkish forces have launched operations in the mountains of northern Iraq following simultaneous attacks by Kurdish separatists in southeastern Turkey that killed at least 26 soldiers.
The Kurdistan Workers' Party (PKK), which has waged a decades-long separatist struggle against Ankara, has claimed responsibility for the attacks, which occurred late on Tuesday and early on Wednesday.
A security source said the attacks targeted police and military installations in several locations in Cukurca and Yuksekova in Hakkari province near the border with northern Iraq's semi-autonomous Kurdish region.
The Turkish army responded with an air-supported operation against the fighters in Iraq's northern Qandil mountains, with both airstrikes and soldiers on the ground employed.
"As of now, wide-reaching operations, including hot pursuit operations, are continuing in the region within the framework of international law," Recep Tayyip Erdogan, the Turkish prime minister, told a news conference on Wednesday.
Speaking on Turkish television, Erdogan said that it was "very clear that this terrorist organisation [the PKK] is a piece in the hands of certain powers". He did not elaborate on who those "powers" were.
Erdogan cancelled a scheduled trip to Kazakhstan, while Ahmet Davutoglu, his foreign minister, called off a diplomatic visit to Bosnia and Herzegovina.
Gul vows vengeance
Abdullah Gul, the Turkish president, also took a firm stance on Turkey's right to respond.
"No one should forget that those who make us suffer this pain will be made to suffer even stronger,'' he told reporters
on Wednesday. "They will see that the vengeance for these attacks will be immense."
But a spokesman for the PKK told Al Jazeera that the group had launched its latest attacks in response to a military campaign waged by Turkey since the country's elections in June.
Roj Welat said that at least nine Kurdish children had been killed in Turkish military operations.
"As you know, a while ago, the president of the Turkish republic visited the border area and started a military operation against our forces. As a result guerrilla forces have begun a revolutionary operation [against Turkish security forces]," he said.
Al Jazeera's Anita McNaught, reporting from Istanbul, said fighting was believed to have started after midnight and was still under way.
"There are still pockets of fighting going on as the Turkish military belatedly floods the area with reinforcements and tries to find out exactly where these attacks were launched from and who was behind them," our correspondent said.
McNaught said that Turkish incursions into Iraq were not unprecedented. Turkey's parliament recently extended a mandate for Turkish forces to mount operations in northern Iraq, which Turkey says the PKK uses as a base for operations into Turkey.
The Turkish government also has an acceptance agreement with the Iraqi government to allow for such "hot pursuit" operations.
However, both the central government in Baghdad, and the regional Kurdish authorities, have condemned the Turkish raids as a violation of Iraqi sovereignty.
"It's part of an ongoing, grinding, almost endless conflict in Turkey's southeast." our correspondent said.
Jabbar Yawar, a security spokesman for northern Iraq's semi-autonomous Kurdistan region, denied the presence of Turkish forces in the region, insisting that all clashes had taken place in Turkish territory.
"There [are] no Turkish forces inside Kurdistan," he told Al Jazeera.
The deaths come a day after a landmine explosion, also in the southeast, killed eight people in an attack which security sources also blamed on Kurdish fighters.Five policemen and three civilians, including a two-year-old girl, were killed in Tuesday's attack. Three injured people were being treated at an intensive care unit.
Security forces combed the area in search of the assailants, believed to be members of the PKK.
Kurdish fighters have carried out a string of attacks in southeastern Turkey in recent months, killing more than 50 Turkish nationals since July and prompting retaliatory air raids on PKK targets in northern Iraq.
The PKK, listed as a terrorist organisation by Turkey and much of the international community, took up arms for an autonomous state in 1984, starting a conflict that has claimed about 45,000 lives.