MOSCOW — The United States and Russia may sign a new nuclear arms reduction agreement in early April, after a previous treaty expired in December, Secretary of State Hillary Clinton said Friday.

“As we speak, our negotiations in Geneva are wrapping up the final elements of the START treaty,” Clinton said in an interview with Bloomberg TV in Moscow. “We hope to have a signing ceremony between President Medvedev and President Obama in early April.”

Clinton later told reporters that only “technical issues” remain to be resolved.

The two governments are trying to agree on the first new treaty in two decades to reduce the number of nuclear weapons and the air and sea vehicles used to deliver them. Presidents Dmitry Medvedev and Barack Obama called in July for a reduction of the two countries’ arsenals to between 1,500 and 1,675 deployed warheads and between 500 and 1,100 missiles, bombers and submarines.

The United States is also seeking Russian support for tougher measures at the United Nations to pressure Iran to stop any development of a nuclear weapon and engage in talks on the scope and intent of its nuclear work.

Clinton said it is hard to verify if Iran is closer to acquiring a nuclear weapons capability than when President Obama took office last year.

“It’s difficult to place timetables or milestones” on how far Iran may have come with clandestine activities, she said in the interview Friday.

Asked if a lack of evidence that Iran is close to producing a weapon could undermine international support for sanctions to rein in its nuclear program, Clinton said the sanctions push “is making progress” and that she had a “receptive audience” in her meetings with Russian leaders the past two days.

Russian Foreign Minister Sergei Lavrov said sanctions “rarely work, but there are situations in which they become unavoidable.” Such a situation “could emerge in Iran,” he told reporters Friday. Medvedev said this month that Russia is ready to consider sanctions that wouldn’t hurt civilians.

During her visit, Clinton urged her Russian hosts to delay plans to bring a nuclear power station into operation in Iran, saying “we want to send an unequivocal message to the Iranians.” Russian Prime Minister Vladimir Putin said the Russian-built Bushehr plant’s first reactor may begin work this summer.

The U.S. is building support for “a regime of smart sanctions, as President Medvedev has referred to them, that will try to change the behavior of the Iranian leadership,” Clinton told reporters after a meeting with the Russian leader.