The U.S. has sent a message through Russia to Iran that the upcoming six-nation negotiations in April are its “last chance” to avoid military action, a Russian diplomat told the Russian daily Kommersant.

Hillary Clinton, the U.S. Secretary of State, relayed the warning to Russian Foreign Minister Sergei Lavrov at the UN Security Council meeting in New York on Monday, the diplomat said, since “Washington does not maintain its own relations” with Tehran.

The diplomat also said there was a likelihood that war would begin "before the end of the year."

"The Israelis are, in essence, blackmailing [U.S. President Barack] Obama. They are putting him in a difficult position: either he supports war or he himself will lose the support [of the influential Jewish lobby].”

There was no immediate response to the report from the U.S. State Department, The Telegraph reports. However, Sergei Ryabkov, a deputy foreign minister, told Kommersant that such threats were “unprofessional” and that “there is never a last chance.”

Despite Russia’s anti-war stance on Iran, it has prepared for the possibility of a war, which would bring with it the problems of huge refugee influx, as well as the possible re-ignition of the Armenia-Azerbaijan Nagorno Karabakh dispute. The contingency plans are classified, according to RT.

The P5+1 group of countries (the U.S., Britain, France, Russia, China, and Germany) accepted an offer last week from Tehran for fresh talks on its nuclear program, which the West and the IAEA fears is a front to create a nuclear weapon, Reuters reports. Iran continues to claim it is only trying to develop nuclear power for civilian purposes. Israel has also indicated it could launch a unilateral attack.