U.S. Under Secretary of State for Political A
U.S. Under Secretary of State for Political A Reuters

The United States wants India and other countries to wait for a final nuclear deal between Iran and world powers before actively engaging with Tehran, the chief American negotiator said on Wednesday, according to Reuters.

"I would say 'hold your horses'. We are not quite to an agreement yet," said Under Secretary Wendy Sherman, referring to India and other buyers of Iranian oil that want to increase their trade ties with Tehran.

Diplomats are negotiating to fill the gaps in an April 2 framework agreement that would curb Iran's nuclear program, allaying Western fears it could develop an atomic bomb, in return for relief from international sanctions.

However, the United States has said that further tough negotiations lie ahead and no guarantees that a deal will be secured by a June 30 deadline.

"We understand that nobody wants to be last in line, everybody wants to be first in line, if the sanctions do get relieved," said Sherman, who has been negotiating on behalf of the United States in the long-running Iran nuclear talks, according to Reuters.

An Indian delegation recently visited Iran to renew talks on seeking development rights of Farzad B gas field and enhancing oil supplies if a deal is clinched by the end of June, the news agency noted.

A delegation-led by Iran's oil minister, Bijan Zanganeh, visited China earlier this month seeking to mend fences with Chinese energy firms to get oil and gas development projects going and discuss oil sales.

Sherman said terrorism and human rights related sanctions against Iran would not be lifted even if a deal was achieved by June 30, indicating that Washington was worried by Iran's influence across the Middle East from Iraq to Lebanon and Syria to Yemen.

Iran-backed Houthi rebels have strengthened their grip over parts of Yemen after seizing the capital Sanaa in September, while Tehran is fighting alongside President Bashar Al-Assad's army in Syria's civil war.

"We are still quite concerned about state-sponsored terrorism, we are quite concerned about human rights, we are quite concerned by what is happening in Yemen, what's happening in Syria, other parts of the world, Lebanon," said Sherman, according to Reuters.

"There are a lot of details that have to be worked out, and there are a lot of events happening in the world, and those events could derail the agreement," she added.

When asked if the economic sanctions against Iran will be lifted in one stroke after a deal, she said, "It will take some time, even after an agreement, for all the implementation to be worked out".

Tensions arose between the United States and Iran after the preliminary framework was reached, as Iran recently accused the United States of "fraud" and "psychological warfare" in publishing a fact sheet announcing what the U.S. claims was agreed on in the framework deal and which an Iranian official called a false translation.

Iran's Supreme leader Ayatollah Ali Khamenei, who will have the final say on any deal, plunged the accord into doubt last week suggesting that "nothing is binding" while President Hassan Rouhani demanded that sanctions be immediately lifted when any deal is signed.

Nevertheless, Secretary of State John Kerry said earlier this week that the world is "closer than ever" to reaching a comprehensive nuclear deal with Iran, though he admitted that key issues remain unresolved.