"This reflects the weakness and desperation of these leaders as they face internal challenges, and an inability to communicate effectively internationally in order to build international support," he added.

The moves came after the US expelled the Bolivian ambassador to Washington, which in turn came after Evo Morales, the Bolivian president, expelled the US ambassador from La Paz, accusing him of instigating violent protests in Bolivia.

The expulsions have sparked a diplomatic crisis in North and South America.

On Friday, Honduras said it would indefinitely postpone accrediting the US ambassador in support of Bolivia and Venezuela.

Bolivia crisis

At least eight people were killed on Thursday in clashes between anti-government protesters and Morales' supporters.

Protests have erupted in several
regions of Bolivia [Reuters]
Morales had earlier accused the US ambassador to Bolivia of supporting protests by led by rebel state governors demanding greater autonomy and opposing Morales' plans to give more land to the poor.

"Charges levelled against our fine ambassadors by the leaders [of] Bolivia and Venezuela are false and the leaders of those countries know it," McCormack said.

On Friday, protests that have continued for several days abated, although tensions remained high.

Despite having earlier ruled out an armed response to the protests, Morales government imposed martial law in the eastern province of Pando on Friday, as demonstrations there contined.

Tit-for-tat expulsions

The US treasury department said the Venezuelan officials whose assets were frozen on Friday were bing targeted as they were believed to have ties to the Revolutionary Armed Forces of Colombia.

The US sanctions and Chavez's threat to halt oil sales to the US plunged ties between the two their lowest point in years.

The diplomatic row highlights the souring relations between the US and South American countries.

Chavez gave Patrick Duddy, the US envoy in Caracas, 72 hours to leave the country, making the announcement on state television and saying at the time that he would be recalling his ambassador from Washington.

He made the announcement hours after saying that his government had detained a group he said were involved in a US-backed plot to overthrow him.

Chavez's critics accuse him of trying to create instability in an attempt to shore up what they say is his plummeting popularity ahead of elections.

Russian bombers

Russia has sent two strategic bombers to
Venezuela [EPA]
Tensions between the US and Venezuela had already risen after Russia sent two strategic bombers to Venezuela for military exercises.

Chavez said the aircraft had arrived to counter US influence in the region.

The Russian move is reported to be Moscow's first strategic deployment in the Western hemisphere since the end of the Cold War and comes amid increased tensions between Russia and the US over the recent conflict with Georgia.

Moscow remains angry that US used military vessels to carry aid to Georgia during Russia's intervention there.