By Steve Holland, Andrew Mills and Parisa Hafezi WASHINGTON/DOHA/ISTANBUL (Reuters) - U.S. President Donald Trump announced on Monday a complete ceasefire between Israel and Iran, potentially ending the 12-day war that saw millions flee Tehran and prompted fears of further escalation in the war-torn region.

As Mr. Trump last week weighed whether to use direct military force against Iran, a bipartisan contingent of lawmakers demanded that the president seek congressional approval before moving forward with any action.

The Israeli prime minister had set in motion plans to attack Iran long before President Trump began efforts to resolve nuclear concerns through negotiations.