By Steve Holland and Andrea Shalal
WASHINGTON, Feb 27 (Reuters) - U.S. President Donald Trump expressed disappointment on Friday about U.S. negotiations with Iran over its nuclear program and warned that "sometimes you have to use force," amid a massive military presence in the region that could presage strikes on the Islamic Republic.
Trump has increased diplomatic and military pressure on Iran in the weeks since an Iranian crackdown on protesters, attempting to force the country's rulers to forswear nuclear weapons and other activities Washington sees as destabilizing.
After the latest round of talks on Thursday in Geneva ended with no deal, Trump's patience appeared to be wearing thin, although he said he had not made a final decision on use of force.
"They cannot have nuclear weapons. And we're not thrilled with the way they're negotiating. We'll see how it all works out," Trump told reporters as he left the White House on a trip to Texas.
Iran denies it is seeking to develop nuclear weapons and wants any accord to include the lifting of U.S. sanctions against it.
Trump spoke a day after negotiations between U.S. envoys Steve Witkoff and Jared Kushner and Iranian officials in Geneva ended without news of a deal although Omani Foreign Minister Sayyid Badr Albusaidi, who was a mediator, said the talks made significant progress.
A big U.S. military force, including two aircraft carrier groups, is in the region waiting on Trump's order.
While Trump's timing for a final decision is unclear, the State Department said Secretary of State Marco Rubio is to hold talks in Israel with Israeli Prime Minister Benjamin Netanyahu on March 1 and 2.
The United States joined Israel’s bombing campaign against Iran in June, striking major nuclear facilities.
Asked about the potential for use of force, Trump said the United States has the greatest military in the world.
"I'd love not to use it but sometimes you have to," he said.
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Trump said more discussions on Iran would take place later in the day.
He did not specify with whom, but Oman, which has been acting as a mediator between the two countries, sent its foreign minister to Washington on Friday for discussions on the issue with U.S. Vice President JD Vance, according to a source familiar with the matter.
Top U.S. defense officials were at the White House on Thursday for talks.
"We want no nuclear weapons by Iran and they're not saying those golden words," Trump said. That appeared to refer to U.S. insistence Tehran commit to not developing nuclear weapons, something the U.S. president made explicit in his State of the Union speech on Tuesday.
Trump planned events in Corpus Christi, Texas, later on Friday and then was to fly on to Palm Beach, Florida, for the weekend at his Mar-a-Lago club.
A source briefed on the internal White House deliberations told Reuters that Trump is “very clear-eyed on all the options before him.”
There is a recognition internally that taking on Iran would be more difficult than the U.S. capture of Venezuelan leader Nicolas Maduro, and there was also internal pessimism as to whether negotiations will bear fruit, the source said.
"Nobody is super optimistic about the negotiations," the source said.
(Reporting by Steve Holland and Andrea Shalal, writing by Bhargav Acharya; Editing by Doina Chiacu, Alistair Bell, Don Durfee and Cynthia Osterman)
