As Iran retaliates, largest US military base in Middle East hit by ballistic missile, Qatar says

Israel said it struck three sites where gatherings of the Iranian regime were taking place, claiming it "eliminated" what it called "several senior figures essential" to the regime, according to an Israeli military official.

Israel worked for thousands of hours to build as valuable and extensive a target bank as possible, according to the official.

"The [Israel Defense Forces] have begun a flyover and is currently striking missile launchers in Iran to thwart the threat posed to the State of Israel," according to an Israeli military official.

Sec. Rubio told lawmakers in a Gang of 8 classified briefing last week that President Donald Trump had not made up his mind about potential military action against Iran, two sources told ABC News.

One source said there were still several outstanding questions during last week's briefing including whether this would be a joint military operation and whether the U.S. would be able to coalesce other nations.

Rubio made the rounds on Friday to members of the Gang of 8 to inform them the operation was in fact a go, sources said.

The Gang of 8 is comprised of leaders from both parties from the Senate and House of Representatives and the chairs and ranking minority members of the Senate and House committees for intelligence.

-ABC News' Rachel Scott and Anne Flaherty

China said it is "highly concerned" over the military strikes launched by the U.S. and Israel on Saturday, calling for an immediate stop to the military action.

"Iran’s sovereignty, security and territorial integrity should be respected. China calls for an immediate stop of the military actions, no further escalation of the tense situation, resumption of dialogue and negotiation, and efforts to uphold peace and stability in the Middle East," a spokesperson for China's Foreign Ministry said in a statement.

-ABC News' Karson Yiu

Sen. Tim Kaine, D-Va., is calling on the Senate to return to Washington immediately to vote on a war powers resolution to check the president's authority to wage war with Iran, calling the military action "idiotic."

“Has President Trump learned nothing from decades of U.S. meddling in Iran and forever wars in the Middle East? Is he too mentally incapacitated to realize that we had a diplomatic agreement with Iran that was keeping its nuclear program in check, until he ripped it up during his first term?," Kaine said in a statement Saturday.

“For months, I have raised hell about the fact that the American people want lower prices, not more war—especially wars that aren’t authorized by Congress, as required by the Constitution, and don’t have a clear objective. These strikes are a colossal mistake, and I pray they do not cost our sons and daughters in uniform and at embassies throughout the region their lives," he added.