Western powers stepped up pressure on Iran on Friday, as Israel's Prime Minister Benjamin Netanyahu and US President Barack Obama stressed their "shared goal" to stop Iran getting a nuclear bomb.

Netanyahu, who is in New York to attend the UN General Assembly, followed up on his demand for a "clear red line" to be drawn on Iran's nuclear drive with a telephone call to the US president focused on the nuclear showdown.

And, in a more sure to infuriate Tehran, the US State Department said it had removed an exiled Iranian opposition group, the People's Mujahedeen of Iran, from its list of designated terrorist organizitions.

Secretary of State Hillary Clinton's decision to take the Mujahedeen-e-Khalq or People's Mujahedeen of Iran (PMOI) off the terror list will increase its fund raising clout in the United States and annoy Tehran.

"Property and interests in property in the United States or within the possession or control of US persons will no longer be blocked, and US entities may engage in transactions with the MEK without obtaining a license," the State Department said.

Iran, meanwhile, demanded the UN Security Council act after it was hit by cyber-warfare and a series of Iranian nuclear scientists were assassinated in attacks it blames on Israel and the United States.

According to a White House statement, Obama and Netanyahu "underscored that they are in full agreement on the shared goal of preventing Iran from obtaining a nuclear weapon."

They "took note of the close cooperation and coordination" between the United States and Israel on "the threat posed by Iran" and agreed to continue regular consultations, the statement added.

Netanyahu grabbed the world's attention at the UN General Assembly with his fierce attack on Iran and his demand for action to stop it enriching uranium to a level that could make a bomb.

The Israeli used a cartoon drawing of a bomb with a fizzing fuse a graph to represent Iran's progress towards having enough enriched uranium to arm a bomb, and drew a red line across it to mark the limit of his tolerance.

He did not mention Israel's threats to stage a unilateral attack, but said Iran's uranium enrichment plants were a credible "target".

"At this late hour, there is only one way to peacefully prevent Iran from getting atomic bombs -- and that's by placing a clear red line on Iran's nuclear weapons program," Netanyahu told the 193-member UN assembly.

"The red line must be drawn on Iran's nuclear enrichment program because these enrichment facilities are the only nuclear installations that we can definitely see and credibly target."

He said Iran could have enough enrichment uranium in the next 12 months to move on to the final stage of making a bomb.

"Faced with a clear red line, Iran will back down," Netanyahu added. "Red lines don't lead to war, red lines prevent war."

Netanyahu and Obama have had a testy relationship, particularly over how to deal with Iran. But Netanyahu welcomed Obama's vow at the UN General Assembly on Tuesday to "do what we must" to stop an Iranian bomb, the White House said.

Iran responded to Netanyahu's speech by saying it would "retaliate" against any military strike.

Without naming Israel or the United States, Iran's Foreign Minister Ali Akbar Salehi said Friday his country has been a victim of "nuclear terrorism."

Salehi said the Security Council, which has passed four rounds of sanctions against Iran's uranium enrichment, should stop using nuclear weapons fears "as a pretext to act as a legislative body."

The council should "utilize its authority to act against those states undertaking cyber attacks and sabotage in the peaceful nuclear facilities and kill nuclear scientists of other countries," Salehi told the General Assembly.

"Any such act committed by a state, as certain countries continue to commit such crimes in my country, is a manifestation of nuclear terrorism," he added.

The United States has denied involvement in the killings of four Iranian scientists since 2010. Israel has refused to comment on the killings.

According to US media, the United States and Israel were behind the Stuxnet computer virus which temporarily crippled Iran's uranium enrichment at its Natanz plant.

The United States is part of a six-nation group which has approved sanctions against Iran while pursuing diplomatic talks on its program. The group has also stepped up warnings to Iran.

Foreign ministers from the United States, Russia, China, Britain, France and Germany met on Thursday on the sidelines of the UN summit and demanded the Islamic state act "urgently" to ease international fears about its plan.

"I call on Iran to stop playing for time. The situation is serious," Germany's Foreign Minister Guido Westerwelle told the UN on Friday.

EU foreign policy chief Catherine Ashton said she would talk with Iranian negotiators to see if new talks are to be held.