TEHRAN, Iran — Iran said Monday that it had halted its most sensitive uranium enrichment work, honoring a deal struck with world powers that has eased concerns over the country’s nuclear program and cleared the way for a partial lifting of sanctions. The announcement in Tehran met a Jan. 20 timetable for the move, which is intended to lay groundwork for a broader accord on Iran’s nuclear activities. The Iranian announcement said inspectors from the International Atomic Energy Agency were present when the enrichment was halted.

In Washington, a State Department spokesman said the United States and its allies would comment further after reviewing an IAEA report on the Iranian action. The move is expected to lead to the lifting of some sanctions on Iran for a six-month period, as well as the freeing of billions of dollars in Iranian assets frozen in Western banks.

Foreign ministers from the European Union meeting in Brussels on Monday agreed to suspend some sanctions immediately.

“This is an important day in our pursuit of ensuring that Iran has an exclusively peaceful nuclear program,” E.U. foreign policy chief Catherine Ashton told reporters.

There was mixed reaction in Iran to the move, which halted the most sensitive uranium enrichment at nuclear plants in the cities of Natanz and Fordo. Iranian opponents of the deal stepped up their denunciations of what they are calling their country’s capitulation to Western demands.

Vatan-e Emrooz, a newspaper closely associated with conservatives, printed Monday’s edition in all black type and dedicated it to coverage of what it called Iran’s “nuclear holocaust.”

Criticism of the deal was not unexpected, but opponents of Iran’s new president, Hassan Rouhani had been uncharacteristically quiet until now.

Ahmad Tavakoli, a prominent conservative member of parliament, told fellow lawmakers Monday that there were two main problems with the nuclear deal.

“First of all, there are so many discrepancies in the text of the agreement that we can hardly be hopeful that our national interests will ever materialize. Second, as officials, we must not reveal our weak points in a way that our enemies can exploit them,” Tavakoli said.