DUBAI, United Arab Emirates — Explosions sent up clouds of dark smoke in the Iranian capital city early Saturday, and Tehran retaliated by firing missiles at Israel as the United States warned of a forthcoming bombing campaign that officials said would be the most intense yet in the weeklong conflict. There was no foreseeable end to the fighting. U.S. President Donald Trump's administration approved a new $151 million arms sale to Israel after Trump said he would not negotiate with Iran without its “unconditional surrender.” Iran's U.N. ambassador said the country would “take all necessary measures” to defend itself. Associated Press video showed explosions flashing and smoke rising over western Tehran as Israel said it had begun a broad wave of strikes. Also early Saturday, loud booms sounded in Jerusalem and incoming missiles from Iran had people heading to bomb shelters across Israel. There were no immediate reports of casualties by Israel’s emergency services. In a sign of the widening nature of the conflict, sirens sounded early Saturday in Bahrain as Iranian attacks tar