Trump said certain conditions had to be met for talks with the Iranians.
In June, Trump announced what he called "hard hitting" sanctions on Iran, including on Supreme Leader Ayatollah Ali Khamenei.
Trump said he is against war despite having the strongest military in the world.
"Our working assumption is that this did not come from Yemen or Iraq", a USA defense official told VOA on Tuesday, adding that a US forensic team is on the ground working with the Saudis to examine the remnants of the missiles.
Trump has offered mixed signals about a possible response to the attack on Saudi Arabia, a USA ally. Trump sends incoherent message The White House would like you to abandon all common sense on "locked and loaded" The same forces that prompted the President to suddenly call off an attack on Iranian targets in June to avenge the downing of a United States drone over the Gulf of Oman seem to be in play now. "If they wanna meet, I'll meet".
Trump's has hinted USA assessment of the attack point to Iran, but stopped short of directly naming the country as US intelligence develops.
Iran-backed Houthi rebels in Yemen have claimed responsibility for the Saturday strikes.
US Secretary of State Mike Pompeo declined to comment specifically on the case, but suggested that the Iranians should be denied because of what he said was the country's "terrorism".
He said the United States does not have any overhead imagery of the attacks, and that it will let the Saudis make their own assessment of what happened.
Iranian President Hassan Rouhani said here Wednesday that Washington should give up "maximum pressure campaign" against the Islamic republic.
Trump explained Monday that sanctions won't be taken off Iran as a requirement for talks, and that's what he meant when he declared "no preconditions".
In another development, the Iranian Foreign Ministry has officially warned the U.S. Interest Section at the Swiss Embassy in Tehran against attributing the attacks to Iran.
In withdrawing the USA from the accord previous year, Trump reimposed sanctions. We are now way ahead of number two and three, which is Saudi Arabia and Russian Federation.
The statement is consistent with Iran's asymmetrical warfare strategy which is based on responding to threats at a time and place the adversaries do not expect.