BEIRUT, April 9 -- Lebanon declared a national day of mourning on Thursday after Israeli strikes pummelled the country, killing nearly 200 people and calling into question the ceasefire between the United States and Iran.

Washington and Tehran had both claimed victory in the Middle East war after agreeing a two-week truce and negotiations aimed at ending a conflict that has killed thousands across the region and plunged the global economy into turmoil.

But fractures emerged quickly, especially when Israel carried out its heaviest strikes yet on neighbouring Lebanon since the Iran-backed militant group Hezbollah joined the war in early March.

At least 182 people were killed and nearly 900 wounded on Wednesday, the Lebanese health minist...