"Iran has long been secretly 'enriching,' in total violation of the terrible 150 Billion Dollar deal made by John Kerry and the Obama Administration," Trump said on Twitter.

"Remember, that deal was to expire in a short number of years. Sanctions will soon be increased, substantially!"

Former secretary of state Kerry spearheaded the diplomacy that led to the 2015 accord between Iran and world powers, the Joint Comprehensive Plan of Action (JCPOA).

The deal promised sanctions relief, economic benefits and an end to international isolation in return for stringent curbs on the Islamic republic's nuclear program.

But Tehran says it has lost patience with perceived inaction by European countries more than a year after Trump pulled the United States out of the agreement, reimposing stinging sanctions.

Tehran announced on Monday it had surpassed 4.5 percent uranium enrichment -- above the 3.67 percent limit under the accord -- though still far below the 90 percent necessary for military purposes.

President Hassan Rouhani said in May that Iran would roll back its commitments under the deal in stages every 60 days in an effort to force the other parties to deliver on their side of the bargain.

As tensions rose, the United States dispatched a naval carrier, bombers and extra troops to the region to counter perceived threats from Iran.

Trump said last month he had called off a retaliatory military strike against Iran at the last minute after the Islamic republic shot down a US drone that it said had crossed into its airspace, a claim denied by Washington.