U.S. Secretary of State Hillary Clinton says the United States and Pakistan must learn lessons from a NATO air assault that killed 24 Pakistani soldiers so the countries can continue fighting terrorism together.

Clinton said Wednesday at a global aid development forum in South Korea that the assault in northwestern Pakistan was tragic. She pledged a quick and thorough investigation.

Clinton also expressed regret over Pakistan's withdraw from a U.S.-backed meeting on Afghanistan taking place next week in Bonn, Germany.

The United States is hoping Pakistan will not play spoiler in the U.S.-backed plan to shore up Afghanistan's security and bring international forces home.