The head of the U.N. nuclear watchdog''s mission to a newly disclosed plant in Iran said on Thursday the inspectors had what he termed a good trip but he declined to give any details.

The site, which Iran revealed last month, has heightened Western fears of a covert program to develop atomic bombs. Tehran says its nuclear program is only for power generation.

"We had a good trip," International Atomic Energy Agency official Herman Nackaerts told reporters on arrival at Vienna airport with the three other members of his team.

"We visited the Fordo enrichment plant. Now we are going to analyze the data and the director-general will then report in due time," Nackaerts said after the four-day trip.

He declined to say whether the team of experts had discovered anything surprising or if they had been able to carry out a full visit of the site, built inside a mountain about 160 km (100 miles) south of Tehran.