Saudi Arabia, Qatar, Iraq and Oman all expressed concern over the U.S. airstrikes on Iranian nuclear sites on Saturday.

Saudi Arabia's Foreign Ministry published a statement noting its "great concern" and expressing the need "to exert all efforts to exercise restraint, de-escalate and avoid escalation" in such "highly sensitive circumstances."

Qatar's Foreign Ministry warned "that the current dangerous tension in the region could lead to catastrophic consequences at both the regional and international levels," while noting its "grave concern" and stressing "the urgent need to halt all military operations and to immediately return to dialogue and diplomatic channels to resolve outstanding issues."

Oman -- which has in the past served as a mediator in talks between Washington and Tehran -- described the American strikes as "illegal aggression" and a "serious violation of international law" in a Foreign Ministry statement posted to X.

Iraqi Foreign Minister Fuad Hussein, meanwhile, said there was a "grave risk posed by attacks targeting religious leaders or nuclear facilities" in Iran, per a readout published on the Foreign Ministry's website.

"Such actions could spark widespread chaos and destabilize the entire region," the readout said, adding that "any strike on Iran's nuclear facilities could lead to a humanitarian and environmental disaster."

Iranian Foreign Minister Abbas Araghchi told reporters in Istanbul, Turkey, on Sunday that President Donald Trump "deceived his own voters" by launching attacks on Iranian nuclear sites, suggesting the president was reneging on his election promise not to get involved in "forever wars."

Araghchi described the American strikes on the Fordow, Natanz and Isfahan sites late Saturday as "outrageous" and laid blame for any fallout on the U.S.

"Washington is solely and fully responsible for the dangerous consequences and far reaching implications of its act of aggression," he said.

Araghchi appeared to close the door on fresh negotiations, saying the path door to diplomacy should always be open but "this is not the case right now."

"It was not Iran, but the U.S. who betrayed diplomacy," Araghchi said. "They betrayed negotiations."

-ABC News' Victoria Beaule

There was no formal "Gang of Eight" briefing for the top leaders of the House and the Senate before the U.S. launched strikes on Iran on Saturday, sources told ABC News, but top Republican members were given details ahead of the action.

Both House Speaker Mike Johnson and Senate Majority Leader John Thune were briefed on the military action before the strikes were carried out, according to people familiar with those conversations.

Democratic leaders -- House Minority Leader Hakeem Jeffries and Senate Minority Leader Chuck Schumer -- were notified of the strike but not given any details, per sources.

One of those sources believed the Democratic leaders were informed only after the military action was underway.

Schumer's spokesperson later told reporters the message came "shortly ahead" of President Donald Trump's announcement, describing it as "a perfunctory notification without any details."

-ABC News' Rachel Scott, Lauren Peller and Allison Pecorin

Iranian dissident groups have responded to the U.S. strikes on Iran's key nuclear sites by reiterating their calls for the toppling of the Islamic Republic and its leader, Ayatollah Ali Khamenei.

Reza Pahlavi, the son of the last Shah Mohammad Reza Pahlavi who was deposed by the 1979 Iranian Revolution, said in a post to X that the American attacks "are the result of the regime's catastrophic pursuit of nuclear weapons at the expense of the Iranian people."

"As Khamenei considers how to respond from his underground bunker, I say to him: For the sake of the Iranian people, respond by stepping down, so the proud Iranian nation can leave the disastrous period of the Islamic Republic behind and start a new chapter of peace, prosperity and greatness," Pahlavi wrote.

Maryam Rajavi, the president-elect of the National Council of Resistance of Iran -- a coalition of dissident Iranian groups that grew out of the People's Mojahedin Organization of Iran, or MEK, revolutionary group that fought against the shah and the Islamic Republic -- said in a statement sent to ABC News, "Now Khamenei must go."

"Khamenei is responsible for an unpatriotic project that, in addition to costing countless lives, has cost the Iranian people at least two trillion dollars -- and now, it has all gone up in smoke," she said.

"No to war -- yes to regime change, i.e., changing the religious dictatorship by the Iranian people and the Iranian Resistance," Rajavi added. "Forward toward a free Iran and a democratic, non-nuclear republic with separation of religion and state and gender equality."