UPDATE: An administration official confirms a second round of talks with Iran and the so-called P5+1 group will occur before month's end. (The P5 = the US, China, Russia, France, and Britain - the permanent members of the United Nations Security Council. The additional country involved is Germany).

For the first time in the Obama administration, top US diplomats sat down with Iranian representatives in Geneva as a sidebar to multi-lateral talks on deterring Iran from developing nuclear weapons.

U.S. Under Secretary of State William Burns, the leader of the US delegation, met with Iran's top negotiator Saeed Jalili.

The meeting marks the most significant US engagement with Iran since ties were severed 30 years ago. The US cut all diplomatic ties with Iran, previously a close financial and military ally in the region, following the 1979 Iranian revolution and subsequent sacking of the US embassy and the taking of  52 Americans hostage. The hostages were held for 444 days and released on Jan. 20, 1981, the day of President Ronald Reagan's inauguration.

This is the frist direct US contact with Iran since multilateral  talks about its suspected pursuit of weapons-grade nuclear material began in 2005.

The US and many of its allies accuse Iran of three violations of United Nations non-proliferation rules, the most recent being the disclosure last week by U.S., British and French intelligence of a covert, underground uranium enrichment facility near Qom. Among the topics on the table today in Geneva is a US demand Iran open the Qom site to immediate international inspection.

Burns took part as an observer in July 2008 when President Bush dispatched him to monitor talks between Iran and the so-called P5 +1 group (the permanent members of the UN Security Council and Germany).

US officials described the Burns-Jalili talks as "significant." At the White House late Wednesday top officials said Burns had the authority to engage in direct talks with Iran, but only if he was convinced they would be "useful."

Iran state media said Jalili arrived in Geneva prepared to tell the US and its allies that it "would by no means be dissuaded of its certain rights." Historically, the words "certain rights" have been linked to Iran's nuclear program.