The White House on Sunday backed Turkey's right to "take action" against Kurdish militants, after waves of air and artillery strikes put a fragile ceasefire between separatists and the Turkish forces in jeopardy.
"Turkey has a right to take action related to terrorist targets," said deputy national security advisor Ben Rhodes after strikes against the outlawed Kurdistan Workers Party (PKK).
"The US of course recognises the PKK specifically as a terrorist organisation," Rhodes said, while welcoming parallel Turkish action against the Islamic State group.
"You have seen of course much more assertive Turkish action in both Syria and Iraq in recent days," said Rhodes.
The strikes on the PKK raise questions about the ceasefire between Kurdish separatists and Turkey, which have been in place since 2013, and could disbalance regional alliances.
Two Turkish soldiers were killed by a car bomb in the Kurdish-dominated southeast of the country late on Saturday, after separatist rebels warned they would no longer observe the truce after Ankara's air strikes.
While the United States has blacklisted the PKK, it has close ties with the Kurdish regional government in northern Iraq, which is also tackling the Islamic State.
"We encourage our different partners in this fight to work together," said Rhodes.
The air strikes came after a week of deadly violence in Turkey that the authorities blamed on both the PKK and the jihadist Islamic State.