Lebanon saw its deadliest day of fighting in months, heaping pressure on stalled U.S.-Iran negotiations while Washington prepares fresh sanctions.

The Israel Defense Forces said Sunday that it killed Abu Hassan Alaa, a senior Hezbollah commander, in southern Lebanon a day earlier. Eleven people died in the Israeli strikes, making them the deadliest since the sides agreed to a ceasefire at the beginning of June.

Israeli Prime Minister Benjamin Netanyahu said the strikes were in retaliation for a Hezbollah attack that injured three soldiers Saturday. Israel said Sunday it would strike the Iranian proxy group again if threatened.