Supreme Leader Ayatollah Ali Khamenei said Iran's nuclear policies would not change despite mounting international pressure against what the West says are Iran's plans to obtain nuclear bombs.

"With God's help, and without paying attention to propaganda, Iran's nuclear course should continue firmly and seriously," he said on state television. "Pressures, sanctions and assassinations will bear no fruit. No obstacles can stop Iran's nuclear work."

As sanctions mount, ordinary Iranians are suffering from the effects of soaring prices and a collapsing currency. Several Iranian nuclear scientists have been killed over the past two years in bomb attacks that Tehran has blamed on its arch-adversary Israel.

In response, Iran has issued a series of statements asserting its right to self-defense and threatening to block the Strait of Hormuz, a vital oil tanker route.

The collapse of the nuclear talks came as Iran seems increasingly isolated, with some experts seeing the Islamic republic's mounting defiance in response to sanctions against its oil industry and financial institutions as evidence that it is in no mood to compromise with the West.

Elections on March 2 are expected to be won by supporters of Khamenei, an implacable enemy of the West.

The failure of the two-day visit by the International Atomic Energy Agency could now hamper any resumption of wider nuclear negotiations between Iran and six world powers as the sense grows that Tehran feels it is being backed into a corner.

In the view of some analysts, the Iranians may be trying to keep their opponents guessing as to their capabilities, a diplomatic strategy that has served them well in the past.

Syrian President Bashar al-Assad's forces rained rockets and bombs down on opposition-held neighborhoods of the city of Homs on Wednesday, reducing buildings to rubble and killing more than 80 people, including two Western journalists.

The barrages marked an intensification of a nearly three-week offensive to crush resistance in Homs, one of the focal points of a nationwide uprising against Assad's 11-year rule and its ferocity has caused international outrage.

More than 60 bodies, both rebel fighters and civilians, were recovered from one area of Homs' Babo Amro neighborhood after an afternoon bombardment, adding to 21 killed earlier in the day, activists.

"Helicopters flew reconnaissance overhead then the bombardment started," Homs activist Abu Abei told Reuters.

Videos uploaded by opposition activists showed smashed buildings, deserted streets, and doctors treating wounded civilians in primitive conditions in Baba Amro district, the main target of Assad's wrath.

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