DUBAI, United Arab Emirates -- Iran on Monday announced the arrest of 17 Iranians accused of spying on the country's nuclear and military sites for the CIA and said some of them have been sentenced to death. President Donald Trump called it "another lie" from Iran.

The arrests happened over the past months, an Iranian intelligence official said at a news conference in Tehran. He said those taken into custody worked on "sensitive sites" in military and nuclear installations. The official did not say how many were given death sentences.

The announcement came amid weeks of rising tensions between Washington and Tehran over Trump's decision to pull the United States out of Iran's nuclear agreement with world powers last year and impose sweeping sanctions on the country.

The official said the 17 were recruited by the CIA and had "sophisticated training" but did not succeed in their sabotage missions. Their spying missions included collecting information at the facilities where they worked and installing monitoring devices, he said.

He said some were staff members at the targeted facilities, and the rest were working as consultants and contractors. The official said the CIA had promised them U.S. visas or jobs in America.

"That's totally a false story. That's another lie," Trump said at the White House.

Trump also said Iran has "disrespected" the United States, adding: "If they want to make a deal, frankly it's getting harder for me to want to make a deal with Iran because they've behaved very badly. They're saying bad things."

U.S. Secretary of State Mike Pompeo, a former CIA director, declined to address specifics of the arrests but said: "The Iranian regime has a long history of lying."

"I think everyone should take with a grain of salt everything that the Islamic Republic of Iran asserts today," he said.