ISTANBUL — Iran’s Supreme Leader on Tuesday ruled out direct negotiations with the United States, a day after President Donald Trump stopped short of directly blaming Iran for a major attack on Saudi Arabian oil installations, allaying, at least for the moment, fears of a military conflict between the two countries.

The comments by Supreme Leader Ayatollah Ali Khamenei appeared to rule out a face to face meeting between Trump and Iranian President Hassan Rouhani at the United Nations next week. “All the officials in the Islamic Republic unanimously believe that there will be no negotiations at any level with the United States,” Khamenei said, according to remarks published on his website.

He said that if the United States returned to the nuclear deal Tehran struck with world powers, then it could take part in negotiations with Iran along with the agreement's other signatories.

Khamenei’s comments came after officials in Washington and Riyadh spent the day analyzing satellite photos and other intelligence that they said indicated that Iranian weapons were used in the assault on the Saudi Aramco facilities. But they presented no new information that would conclusively show that Iran directed or launched the attack, which Saudi officials said led to a 50 percent reduction in oil production.

U.S. officials rejected claims by Houthi rebels in Yemen, who receive Iranian support, that they had launched the strike Saturday, describing it as more sophisticated and powerful than anything the rebels could accomplish on their own.

But neither Trump nor Saudi leaders would say unequivocally that Iran was responsible.

"It's looking that way," Trump told reporters in the Oval Office, during a meeting with Bahrain's crown prince. "As soon as we find out definitively, we'll let you know."

Trump’s reluctance to assign blame appeared to reflect his long-standing desire to keep the United States out of wars, despite his tweet Sunday that the United States was “locked and loaded depending on verification.”

"I'm not looking to get into new conflict, but sometimes you have to," Trump said Monday.

Trump didn’t rule out a military response but made clear that the Saudis would take the lead — and pay the bill.

"The fact is that the Saudis are going to have a lot of involvement in this if we decide to do something. They'll be very much involved, and that includes payment," Trump said.

For their part, Saudi officials affirmed that Iranian weapons were used in the attack but also stopped short of singling out Iran in statements that appeared to reflect fears across the Persian Gulf of a wider and more violent conflagration.

Col. Turki al-Malki, the spokesman for the Saudi-led coalition fighting in Yemen, said initial investigations into the strikes on the oil facilities had found that “these weapons are Iranian weapons.” He added that the attacks “did not originate in Yemeni territory as claimed by the Houthi militias.”

Malki said that investigators were continuing to determine the origin of the attacks and that the final results, including a display of weapons remnants, would be publicly shared "soon."

"We have the ability to secure vital and economic installations," Malki said. "But we are dealing with a terrorist attack from terrorist groups."

A Saudi Foreign Ministry statement released later Monday said the kingdom was inviting United Nations and international experts "to view the situation on the ground and to participate in the investigations."

"The Kingdom will take the appropriate measures based on the results of the investigation, to ensure its security and stability," the Foreign Ministry said in its statement, which also called for an international response to what it deemed a threat to "global energy supplies."

U.S. military investigators arrived at the attack sites in Saudi Arabia within the past day and were gathering intelligence to learn more about the weapons used, a U.S. official said Monday.

Pentagon officials have urged restraint in any response, arguing against a potentially costly conflict at a time when the U.S. military is seeking to reduce its Middle East footprint, officials familiar with the conversations said Monday.

American officials were working under the assumption that the strikes did not emanate from Yemen, nor do they believe that the attacks were launched by Tehran's allies in neighboring Iraq, said the official, who was familiar with discussions about the attacks but was not authorized to speak publicly.

Senior U.S. officials were continuing to deliberate over how to respond.

Iran denied any involvement. China and European countries warned against hastily assigning blame.

The Houthi rebels warned foreigners to leave the area of Saturday’s attacks, which targeted installations belonging to the state-owned oil company, Aramco. The facilities could be targeted again at “any moment,” a Houthi military spokesman said.

"We assure the Saudi regime that our long hand can reach wherever we want, and whenever we want," spokesman Yahya Saree said in a statement, adding that drones modified with jet engines were used in the operation Saturday.

The Houthis, who seized Yemen’s capital from the internationally recognized government in 2014, have been fighting a devastating war against a Saudi-led coalition in Yemen and, according to U.S. and Saudi officials, have received military and logistics support from Iran.

The Houthis also have not provided any proof to support their assertion that they carried out the strikes using what they said was a fleet of 10 drones.

"We don't need to provide evidence," Mohammed Albukhaiti, another Houthi spokesman, said in a phone interview Sunday.

For its part, Russia has cautioned against assigning blame too quickly to Iran and taken the opportunity to offer its stae of the art antiaircraft technology for sale to Saudi Arabia.

“We are ready to offer Saudi Arabia necessary assistance, and the Saudi political leadership will suffice to make a wise government decision, as Iranian leaders once did, buying S-300 systems and as did (Turkey’s) President Erdogan, purchasing from Russia the most advanced S-400 Triumph air defense systems,” President Vladimir Putin said at a press conference.

Russia, which has benefited from the rise in oil prices brought on by the attacks, has not said if it will increase productions levels to make up for any shortages.

Brian Hook, the State Department's special representative for Iran, spoke with congressional staffers from the national security committees about the situation in a call Monday afternoon. When asked about the impact of the strike on the kingdom, Hook responded that the Saudis consider it to be "their 9/11," according to two people familiar with the call. The comparison to the terrorist attacks in the United States, in which 15 of the 19 hijackers came from Saudi Arabia, rankled several staffers, said the two people, who spoke on the condition of anonymity to discuss the details of a private briefing.

Congressional leaders have asked administration officials to hold a briefing on the attack for lawmakers. An aide on the House Intelligence Committee, who spoke on the condition of anonymity to discuss ongoing negotiations, said that is expected to take place later this week.

The Washington Post’s Will Englund in Moscow; Louisa Loveluck in Baghdad; Charles Maynes in Moscow, Ali Al-Mujahed in Sanaa, Yemen; and Anne Gearan, Steven Mufson, Missy Ryan, Dan Lamothe, Karoun Demirjian and Carol Morello in Washington contributed to this report