Pakistan, May 27 -- US forces attacked missile sites in southern Iran and boats trying to lay mines on Monday, US Central Command said, imperiling a fragile ceasefire and casting new doubt on a deal to end the Middle East war.

The strikes came as top Iranian negotiators arrived in Doha for the latest round of talks to end the months-long conflict, and as the Israeli military stepped up hostilities with Iran-backed Hezbollah in southern Lebanon.

Iranian media said on Tuesday that Tehran's negotiators were seeking the release of around $24 billion in frozen assets abroad.

"US forces conducted self-defense strikes in southern Iran to protect our troops from threats posed by Iranian forces," Tim Hawkins, a Central Command spokesman, said i...