Iran says it is installing centrifuges with "better quality and speed" to improve the uranium enrichment process at its nuclear plants.
The foreign ministry statement comes despite international demands for Iran to halt its nuclear activities.
It said the UN atomic watchdog had "full supervision" of the centrifuges.
The US, UK and other Western nations have long believed Iran's nuclear programme is aimed at developing atomic weapons - a claim rejected by Tehran.
Tehran says it is refining uranium for electricity generation and medical applications.
Enriched uranium can be used for civilian nuclear purposes, but also to build atomic bombs.
'Peaceful' activity
"By installing the new centrifuges progress is being made with more speed and better quality," said spokesman Ramin Mehmanparast.
He said the move showed Iran's success in pursuing its "peaceful nuclear activity".
Six world powers are negotiating with Iran over its nuclear programme, and the country is subject to United Nations Security Council sanctions over its refusal to halt uranium enrichment.
Last month, the British government accused Iran of testing missiles capable of carrying a nuclear warhead, in contravention of a UN resolution.
The Iranians openly test-fired 14 surface-to-surface missiles with a range of 2,000km (1,250 miles) as part of a 10-day programme of military exercises.
Its foreign ministry said none of these missiles had had nuclear capability.
