European foreign policy chief Javier Solana voiced concern on Monday about Iran's latest missile tests, Reuters reported.
"Everything that is done in that context is a concern," said Solana, who will head the Western delegation in talks with Iran in Geneva on Thursday.
Earlier on Monday, Iran test-fired a missile which defense analysts have said could hit Israel and U.S. bases in the Gulf, a move likely to further irk world powers ahead of Thursday's talks.
Solana said last week's disclosure by Tehran that it is building a second uranium enrichment plant was something that had to be resolved "immediately" with the International Atomic Energy Agency (IAEA), the U.N. nuclear watchdog.
When asked what sanctions Iran should face if it failed to comply with Western demands over its nuclear programme, Solana said "now is not the time to talk about that."
Speaking on the sidelines of a meeting of European Union defense ministers in Sweden, he said the aim of Thursday's talks was "engagement, engagement."
Western powers are demanding that Iran abandons a nuclear programme they believe is aimed at developing nuclear arms, but which Iran says is for peaceful energy production. The powers have offered incentives if Iran complies and threatened more sanctions if it does not.
U.S. President Barack Obama said on Saturday the discovery of a secret nuclear plant in Iran showed a "disturbing pattern" of evasion by Tehran. He warned Iran on Friday it would face "sanctions that bite" unless it came clean.
Iran has rejected Western condemnations of the plant's construction, saying the facility near the holy city of Qom is legal and open to inspections by the IAEA.