The move could increase pressure on Iran from western nations which want it to cease nuclear activities and could end with Tehran's referral to the United Nations Security Council for possible sanctions.
The UN's atomic watchdog has confirmed the seals were removed at Iran's Natanz atomic research facility, under supervision by the agency's inspectors.
The international community is concerned that Iran is building nuclear weapons, but Tehran insists it is merely working on a peaceful nuclear program for energy production purposes.
Talks between the European Union trio of Germany, France and the UK broke off last August after Tehran resumed uranium conversion activity after suspending such activity in 2004.
Deputy head of Iran's Atomic Energy Organisation announced the development.
"Today, with the powers delegated to IAEA inspectors in Iran, some of the seals that are in the field of only research were removed, and research facilities resume their work," Mr Saeedi said.
He stressed Iran is not resuming the production of nuclear fuel, a process that would involve uranium enrichment.
"What we resume is merely in the field of research, not more than that," he said.
"We make a difference between research on nuclear fuel technology and production of nuclear fuel. Production of nuclear fuel remains suspended."