The United States has asked Russia to inform Iran's leadership that forthcoming talks with six world powers over its nuclear programme represents Tehran's last chance, a Russian daily reported on Wednesday.

The Israelis are de-facto blackmailing (President Barack) Obama. They put him into an interesting position: either he backs the war or loses the support (of the U.S. Jewish lobby), the well-connected Kommersant newspaper quoted a Russian diplomatic source as saying.

Speculation has been growing in recent months that Israel, with or without U.S. support, could launch some form of strike against Iranian nuclear installations.

The P5+1 group of countries comprised of the United States, Britain, France, Russia, China and Germany accepted an offer last week from Tehran for fresh talks on its nuclear programme, which the West fears is a front to create a nuclear weapon.

Iran, which denies seeking nuclear weapons, offered to bring unspecified new initiatives to the table.

The Americans are insisting that it (the meeting) is the last chance for Tehran, Kommersant said. Such a position, the source told Kommersant, was stated by Hillary Clinton at talks with (Russian Foreign Minister) Sergei Lavrov. She also asked her Russian colleague to pass on this message to Iranian authorities with whom Washington does not have any links.

The foreign ministry was not available for comment. But Kommersant quoted Deputy Minister Sergei Ryabkov as saying that passing on such a message would be unprofessional.

The date and the venue for the talks are yet to be agreed. The diplomat told Kommersant they would take place in April.

The unnamed diplomat said a strike on Iran could happen before the end of the year.

U.S. Defense Secretary Leon Panetta has said the United States would take military action to prevent Iran from acquiring a nuclear weapon if diplomacy failed.

Panetta was reported in February by David Ignatius, a Washington Post columnist who specializes in intelligence, as believing there was a strong likelihood that Israel would attack Iran's nuclear program within the next six months.

(Reporting by Gleb Bryanski)