GENEVA (AFP) - A US envoy held one-on-one talks with Irans top nuclear negotiator for the first time Thursday during a critical meeting with five other world powers hoping to convince Tehran to freeze its atomic drive. Irans top nuclear negotiator met officials from the United States, Russia, China, Britain, France and Germany, the countries known as P5+1, in a villa overlooking Lake Geneva only a week after a new secret Iranian uranium enrichment plant was disclosed. Iranian missile tests this week also rattled international nerves. The US envoy at the talks, William Burns, also met separately with Iranian negotiator Saeed Jalili, in a rare official encounter between representatives of the arch-foes, a US spokesman said. US State Department deputy spokesman Robert Wood refused to reveal details of the encounter, but it highlights the new engagement policy favoured by US President Barack Obama since he succeeded George W Bush in January. It is the first time that Iranian and US officials holds direct talks on a bilateral issue since the two sides broke relations 30 years ago, although meetings took place during the Bush years to discuss Iraq and Afghanistan, a US official said. The talks with the UN Security Councils five permanent members and Germany provide Iran an opportunity to come clean about its nuclear ambitions, Wood said. But he warned that US patience has its limits. This is the first time that weve agreed to sit down with Iran as a full member of the P5+1 discussions, he told journalists. Were willing to engage in this process but were not going to do it forever. Theres going to come a point when were not going to engage, he said. Meanwhile, Foreign Minister Manouchehr Mottaki discussed Irans nuclear programme with two leading US Congressmen while on a rare visit to Washington, the official IRNA news agency reported on Thursday. Wednesdays meeting on the eve of long awaited nuclear talks in Geneva between Iran and six world powers, including the United States, involved discussion of Irans new atomic site near Qom, IRNA said in a report from New York. The two Congressmen asked Mottaki whether Iran would allow access to the new uranium enrichment plant soon, IRNA said. Mottaki responded: Iran has always cooperated with the (IAEA) Agency and is also now ready to allow inspectors to visit the plant. He said the date for the inspection would be fixed in talks with the IAEA. Washington insisted that no administration officials would meet Mottaki during his brief visit but that did not rule out talks with lawmakers. The IRNA report did not name the two Congressmen, saying only that they were members of the Foreign Relations Committee. At the meeting, Mottaki reiterated that Iran would not give up its rights under the Non-Proliferation Treaty to master the nuclear fuel cycle for peaceful purposes, but added that Iran has no plans to quit the NPT.