By Liu Dong

Six major global powers wrapped up Wednesday a "very constructive" ambassador-level meeting at the United Nations on pushing newly crafted UN sanctions to curb Iran's nuclear ambitions, marking the first substantive initiation of negotiations.

"We have just had a very constructive consultation," Li Baodong, China's UN ambassador, said after the closed-door meeting, attended by envoys from the five veto-wielding UN Security Council (US) members plus Germany.

Li's words were echoed by French, British and Russian ambassadors. "All six countries are onboard. We are getting into the substance," said French Ambassador Gerard Araud.

"We now have a better understanding of each other's positions. We will continue these consultations," Li added.

The US sanctions proposal, incorporating comments from concerned sides, based on which the negotiation focused, was categorized into five dimensions: a comprehensive arms embargo, investment check in the energy domain, financial curbs, granted power to seize Iranian smuggling ships, and penalties on the Revolutionary Guards, according to diplomats.

The five-pronged paper is under discussion in a series of secret meetings in New York between Britain, France, Germany, Russia, China and the US, known as the E3+3, London's The Times reported.

Russia and China have partially supported the draft, voicing opposition on energy investment bans and held reservations on authorizing seizures of cargo containing materials linked to Iran's nuclear program.

"All the major powers are currently engaged in a fierce interest-bargaining," Yin Gang, an Iran expert at the Chinese Academy of Social Sciences, told the Global Times.

"China has to display responsible power in the global arena by conforming to the nuclear non-proliferation regime. Furthermore, China should restrain from adopting stringent measures to aggravate the problem," Yin said.

"China maintained its consistent stance to address the Iran nuclear issue and will not follow the West. China's vote will depend on the specific content of the draft," Yin added.

The complexity led diplomats to expect a prolonged discussion process, indicating that a vote by the full 15-member council might be pushed back until June, despite the US' stepped-up efforts to push the adoption prior to the end of April, citing urgency to restrain Iran's accelerated nuclear activities.

A top US military officer claimed that Iran was capable of producing adequate highly enriched uranium for a nuclear bomb within one year, while a complete nuclear weapon will take 3-5 years.

A bipartisan group of 363 House lawmakers sent a letter to President Barack Obama on Wednesday urging him to impose "crippling" sanctions on Iran with or without UN action to fulfill his 2008 campaign pledge to "prevent Iran from obtaining a nuclear weapon," The New York Times reported.

In a move to combat the escalated pressure, Iran filed a complaint Tuesday with the UN, chiding the United States over infringement of the UN charter with an atomic attack threat.