Israel targeted Evin prison in Tehran on Monday, one of the most potent symbols of Iran's governing system, in what Israel called the most intense bombing yet of the Iranian capital, a day after the United States joined the war by blasting nuclear sites.

Iran repeated earlier threats to retaliate against the United States. But it had yet to do so in a meaningful way more than 24 hours after U.S. bombers dropped 30,000 pound bunker-busters on its underground nuclear sites, while U.S. President Donald Trump openly mused about overthrowing the Iranian government.

Oil prices barely budged on the first trading day after the U.S. joined the war, suggesting traders doubted Iran would follow through on threats to disrupt oil supplies from the Gulf.