LAUSANNE, Switzerland, March 29-- Foreign ministers from major world powers on Sunday night kicked off a plenary session to further bridge gaps on Iran's potential nuclear framework deal.

The negotiation, chaired by EU foreign policy chief Federica Mogherini, joined by Chinese Foreign Minister Wang Yi, U.S. Secretary of State John Kerry, Russian Foreign Minister Sergey Lavrov, French Foereign Minister Laurent Fabius, British Foreign Secretary Philip Hammond as well as German Foreign Minister Frank-Walter Steinmeier.

The session marks the first meeting of top diplomats from P5+1 countries (namely the United States, Britain, China, France, Russia and Germany) in the "final stage" of the nuclear talks which resumed since Thursday, a sign that a possible framework agreement might be within reach.

A series of bilateral talks between foreign ministers were taking place over the last two days. On Friday, Chinese Foreign Minister Wang Yi held bilateral meetings with his counterparts from Iran, the United States, France, Germany, the EU and Russia.

Wang on Sunday called on all sides to seize the opportunity to show flexibility and political decision to push the Iranian nuclear negotiations into fruition.

From the beginning of 2015, the six major world powers have been negotiating with Iran almost nonstop, round after round and meeting after meeting, in an effort to put Iran's nuclear program under international control in return for easing of sanctions.

On Nov. 24 of 2013, the P5+1 and Iran reached a first-step agreement on Iran's nuclear program, the Geneva 2013 Joint Plan of Action, which demanded Iran suspend some sensitive nuclear activities in exchange of limited sanction relief to buy time for the diplomatic effort to resolve the issue.

Since then, the P5+1 and Iran have twice missed self-imposed deadlines for a final and comprehensive accord, respectively in June and November last year, and the negotiators then set March 31 of 2015 as a new deadline for a political framework agreement and June 30 for the final deal.