Turkey has launched a military operation against Kurdish rebels in northern Iraq after rebels attacked army posts in southeastern Turkey, killing 24 soldiers and wounding 18.

Turkish news reports say air force jets hit Kurdish targets in Iraq while helicopters flew in Turkish soldiers. The reports say the retaliatory attacks killed at least 20 rebels.

Fighters from the Kurdistan Workers Party, or PKK, opened fire on military outposts in Cukurca and Yuksekova in Turkey's Hakkari province.

Turkish Prime Minister Recep Tayyip Erdogan canceled a trip to Kazakhstan Wednesday and said Turkish forces are in “hot pursuit.” President Abdullah Gul said “vengeance for these attacks will be great.” He said those who inflicted pain on the Turks will suffer even more.

U.S. President Barack Obama condemned what he called the “outrageous terrorist attack,” and said the United States will continue its strong cooperation with Turkey as it works to defeat the PKK. A U.S. State Department spokesman said Turkey has the right to defend itself against terrorism. He said the United States will support Turkey when it pursues terrorists in Iraq and elsewhere.

European Union foreign policy chief Catherine Ashton called the attacks “shameful.” Kurdish regional President Massoud Barzani condemned the rebel attacks as “criminal.” United Nations Secretary-General Ban Ki-moon said it is unacceptable that Iraqi territory is being used to launch cross-border attacks against neighboring countries.

The PKK has stepped up attacks against Turkish targets in recent weeks. Turkish forces have responded by increasing the number of airstrikes against suspected rebel bases in northern Iraq. Turkey called on Iraq last week to stop the Kurdish rebels from attacking Turkey from Iraqi soil. It says its “patience is running out.”

Kurdish rebels have waged a campaign for autonomy in Turkey's largely Kurdish southeast since 1984. The fighting has killed more than 40,000 people. Turkey, the United States, and European Union regard the PKK as a terrorist group.

The Turkish government has addressed the demands of Kurds and other minorities for greater rights. Prime Minister Erdogan is pushing to amend the constitution, which was written in 1982 when Turkey was under military rule. But Kurdish leaders say an amended constitution should recognize the Kurds as a distinct element of the nation and grant them autonomy.