It was unclear why Donald Trump chose to issue the proclamation on Wednesday.

President Donald Trump on Wednesday gave the State Department the authority to bar senior Iranian officials and their family members from entering the United States as immigrants or non-immigrants, the White House said in a proclamation.

The proclamation, posted on the White House website and bearing Wednesday's date, repeated U.S. accusations that Iran sponsors terrorism, arbitrarily detains American citizens, threatens its neighbours and carries out destructive cyber attacks.

"Given that this behaviour threatens peace and stability in the Middle East and beyond, I have determined that it is in the interest of the United States to take action to restrict and suspend the entry into the United States, as immigrants or non-immigrants, of senior government officials of Iran, and their immediate family members," Trump said in the proclamation.

Iranian officials were not available to comment.The U.S.-Iranian confrontation has ratcheted up since last year, when Trump withdrew from Iran's 2015 nuclear deal with major powers and reimposed sanctions that have crippled the Iranian economy. Trump wants to go beyond that deal to further curb Iran's nuclear program, halt its ballistic missile work and end its support for proxy forces in the Middle East.

It was unclear why Trump chose to issue the proclamation on Wednesday. Iranian President Hassan Rouhani earlier said the United States would have to "pay more" if it wanted a wider deal and rejected meeting with the U.S. president for now. Both men were in New York for the annual United Nations General Assembly gathering of world leaders.

A State Department spokeswoman, speaking on condition of anonymity, said, "the government of Iran is the world's leading state sponsor of terrorism. The regime has destabilised the Persian Gulf region with attacks on oil and shipping infrastructure.

"Their support for the (rebel) Houthis in Yemen and Shia militias in Iraq and Syria contribute to the regional instability and the humanitarian crises in those countries. The Iranian regime continues to suppress ethnic and religious minorities as well as unjustly detain foreign citizens to perpetuate their foreign policy aims," the spokeswoman said.

"Allowing senior Iranian regime officials or their family members to continue to travel to the United States would be counter to our interests and be seen as turning a blind eye to these actions," she said.

Trump gave the authority to decide who would be covered by the proclamation to the secretary of state, or whomever he or she designates.

Trump also provided exceptions, saying that among others the proclamation would not apply to lawful U.S. permanent residents, those granted asylum, or refugees already admitted to the United States. He also provided possible exceptions for people whose entry "would further important ... law enforcement objectives."