With one eye on his standing at home ahead of March's parliamentary election, Ahmadinejad will meet other anti-American presidents on a trip Washington said showed Iran was "desperate for friends".

His first stop is OPEC-ally Venezuela, where Ahmadinejad has been assured a warm welcome by President Hugo Chavez. He will also visit Cuba and Ecuador and attend the inauguration of re-elected Nicaraguan President Daniel Ortega.

"We are making absolutely clear to countries around the world that now is not the time to be deepening ties, not security ties, not economic ties, with Iran," US State Department spokeswoman Victoria Nuland said on Friday.

"As the regime feels increasing pressure, it is desperate for friends and flailing around in interesting places to find new friends," Nuland said.

US President Barack Obama signed new measures into law on New Year's Eve that will make it harder for most countries to buy Iranian oil. The European Union is expected to announce some form of ban on Iranian oil by the end of the month.

The sanctions are aimed at forcing Iran to halt its nuclear work, which the United States and its allies say is aimed at producing bombs. Iran says it is for power generation only.

The sanctions are already hurting Iranians. Faced with rising prices and a falling rial currency, they have been queuing at banks to convert savings into dollars.

"The representative of the dignified people of Iran will be welcome," Chavez said last week as Iranian naval exercises helped push up global oil prices.

But it remains to be seen how far Chavez would go in backing Iran's threat to close the Strait of Hormuz, the world's most important oil shipping lane, or how much he could undermine the sanctions by providing fuel or cash to the Islamic Republic.

Other regional leaders due to receive Ahmadinejad, such as Ortega and Ecuador's Rafael Correa, have a similar ideological stance to Chavez but fewer resources available to help Iran.

Ahmadinejad, who is subordinate to Supreme Leader Ayatollah Ali Khamenei on foreign policy, has said little about the spike in tensions with the West, leaving it to military commanders to make the most bellicose statements.

Under increasing fire from rival hardliners aiming to stop his supporters making gains in the March election, Ahmadinejad will hope the foreign tour will show voters he still has international clout and is not, as his critics say, a lame duck.

With less than 18 months left of his presidency, he will be keen to preserve his legacy as a leader who stood up to Washington in a changing Middle East.

Copyright Reuters, 2012