Kurdish rebels kill 26 Turkish soldiers in Hakkari
At least 26 Turkish soldiers have been killed in clashes with Kurdish rebels at police and army posts in south-east Turkey, the government says.
The attacks, in the mainly Kurdish province of Hakkari, are thought to have inflicted the biggest loss on Turkish security forces in years.
In response, Turkish troops are reported to have crossed into northern Iraq where the rebels are based.
President Abdullah Gul has vowed a "great vengeance".
The attacks come a day after a blast in the south-east Bitlis province killed five police officers and three others.
President Gul recently visited troops in the region to boost morale in an area that has recently seen a spike in violence by Kurdish rebels.
Turkey has responded to this with a police crackdown on suspected rebel sympathisers and air strikes on Kurdish sites in northern Iraq.
Rebels are seeking greater autonomy in the country's Kurdish-dominated south-east, and have killed dozens of members of the country's security forces, and at least 17 civilians, since mid-July.
Tens of thousands of people have died in the conflict since 1984.
The latest violence - thought to be at least two simultaneous ambushes - took place in Cukurca and the district of Yuksekova overnight on Tuesday to Wednesday.
The ministry of interior said 26 soldiers had died and 16 were injured.
"We have been clashing with the Turkish forces in two areas since around 03:00," Dostdar Hamo, a spokesman for the rebel group, told AP news agency by telephone.
This is the biggest attack in terms of soldiers' loss of life since 1993, says the BBC's Jonathan Head in Istanbul, and the public pressure to respond will be intense.
Turkey's army is a conscript one and many families will have sent sons to serve.
Security sources say Turkish planes are bombing Kurdish rebel bases in northern Iraq, while local news sources say soldiers have also entered the area. Fighter jets and gunships have been leaving the main air base in the south-east.
"No-one should forget that those who make us suffer this pain will be made to suffer even stronger," President Gul told reporters. "They will see that the vengeance for these attacks will be great."
The prime minister and foreign minister had both cancelled overseas trips in response to the bloodshed, reports said.
In response to a mid-August rebel attack in Cukurca which killed nine Turkish soldiers, Turkish jets bombed Kurdish rebel bases in northern Iraq, killing up to 160 rebels, Turkish officials said.
The Turkish government complains that the border with northern Iraq is leaky, allowing rebels to infiltrate with relative ease, our correspondent says.
But previous attempts to pummel rebel bases in northern Iraq have not had the desired effect on rebel activity, he says.
There is little talk now of renewing the so-called "democratic opening", an initiative from two years ago, which aimed to end the conflict in the south-east by expanding the rights of the Kurdish minority, our correspondent adds.