The head of the International Atomic Energy Agency is in Iran for another round of talks aimed at persuading the Tehran government to freeze its nuclear program.
Mohamed ElBaradei's one-day visit comes two days after Iran announced its engineers had successfully enriched uranium to a level used in nuclear power plants.
ElBaradei met Thursday with Iran's nuclear chief, Gholamreza Aghazadeh.
The IAEA chief is to report to the U.N. Security Council on April 28 -- the deadline the council has set for Iran to halt its nuclear activities.
Iranian President Mahmoud Ahmadinejad vowed again Thursday his government will not back away from uranium enrichment, despite international pressure.
The United States accuses Iran of running a secret nuclear weapons program. Iran says its nuclear program is for peaceful energy purposes only.
China says it is sending a top envoy to Iran and Russia in an attempt to defuse Iran's nuclear standoff with the West. The Chinese Foreign Ministry said Assistant Foreign Minister Cui Tiankai will visit the two countries, starting Friday.
Earlier, China expressed concern at the United Nations over Iran's announcement that it has enriched uranium to nuclear power strength. Some information for this report was provided by AFP, AP and Reuters.