Iranian President Hassan Rouhani said on Tuesday U.S. President-elect Trump cannot unilaterally cancel the nuclear deal Tehran signed with world powers including Washington and that talk of renegotiating it was "meaningless".

Trump, who will take office on Friday, has called the July 2015 agreement "the worst deal ever negotiated". He has threatened to either scrap the agreement or seek a better deal.

Under Iran's agreement with the United States, France, Germany, Britain, Russia and China, Tehran agreed to shrink its nuclear programme to satisfy the powers that it could not be put to developing atomic bombs. In exchange, Iran received relief from sanctions, most of which were lifted in January 2016.

"The president elect has shown he is not happy about the nuclear deal, calling it the worst deal ever signed. This is only empty talk," Rouhani told a news conference on the anniversary of the removal of sanctions.

"I don't think he can do much when he goes to the White House," added Rouhani, a moderate who, through the diplomatic opening engineered a thaw in the Islamic Republic's long antagonistic relations with the West.

Rouhani said he was hopeful about the future of the nuclear deal, which has been buttressed by a U.N. Security Council resolution, calling talk about renegotiation "meaningless."

"I am optimistic about the future of the nuclear deal ... (It) is good for the United States, but he (Trump) doesn't understand," said Rouhani, whose remarks were broadcast live on state television.

Rex Tillerson, Trump's nominee for U.S. Secretary of State, said last week that he would recommend a "full review" of the nuclear deal but did not call for an outright rejection.