President Trump did little to calm fears over escalating tensions with Iran on Thursday, saying he hopes the two countries don't go to war.

"Mr. President, are we going to war with Iran?" a reporter asked as Mr. Trump greeted the Swiss president at the White House.

"I hope not," Mr. Trump responded.

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The U.S. pulled most of its personnel from neighboring Iraq as U.S. officials said they believe Iranian combat drivers were responsible for attacks on four oil tankers near the Persian gulf. The U.S. insists the threat posed by Iran is intensifying, even as allies claim that isn't the case.

President Trump welcomes Switzerland's Federal President Ueli Maurer, right, to the White House on Thursday, May 16, 2019, in Washington. Andrew Harnik / AP

Mr. Trump balked at a New York Times report earlier this week that said the U.S. is preparing to send up to 120,000 troops to the Middle East to manage Iran if necessary, but he didn't dismiss the possibility of considering troops in the future if necessary.

"I think it's fake news, OK?" the president told reporters on the South Lawn Tuesday. "Now, would I do that? Absolutely. But we have not planned for that. Hopefully we're not going to have to plan for that. And if we did that, we'd send a hell of a lot more troops than that."

The president also told acting Defense Secretary Patrick Shanahan that he does not want war with Iran, CBS News' David Martin confirmed. The New York Times first reported the remark, which Mr. Trump made during a Situation Room meeting Wednesday.

The U.S. announced earlier this week it's imposing new sanctions on Iran on the one-year anniversary of the U.S. withdrawing from the Iran nuclear deal. Tehran has deemed those sanctions "unacceptable."

"Tehran can expect further actions unless it fundamentally alters its conduct," Mr. Trump said in a statement announcing the new sanctions. "Since our exit from the Iran deal, which is broken beyond repair, the United States has put forward 12 conditions that offer the basis of a comprehensive agreement with Iran. I look forward to someday meeting with the leaders of Iran in order to work out an agreement and, very importantly, taking steps to give Iran the future it deserves."

Some members of Congress, including Mr. Trump's allies, have expressed frustration about not having a clearer idea of what the administration intends to do regarding Iran. Republican Sen. Lindsey Graham told reporters Thursday he had not been briefed about the withdrawal of U.S. personnel from Iraq this week.

"That's disappointing and unacceptable," Graham said about the lack of communication between the administration and members of Congress. "I would tell the administration, you should pick up the phone and call members of Congress so that we don't have a microphone put in our face, ask us about why you're doing something when we have no clue."

On Thursday, Sen. Tim Kaine, Democrat of Virginia, confirmed that the full Senate would be briefed by the administration next week, on Tuesday.

Grace Segers and Alan He contributed to this report.