Washington- US President George W Bush on Saturday urged Congress to approve a long standing free trade agreement with Colombia, warning a failure to do so could encourage populist Latin American leaders pursuing anti-US policies.

"If this agreement were not to pass it would embolden voices of populism in the neighbourhood to the detriment of a government that has been very strong," Bush said at a White House meeting with Colombian President Alvaro Uribe, a close US ally in South America.

Bush was referring to Venezuelan President Hugo Chavez and Bolivian President Evo Morales, two socialist leaders opposed to free trade agreements in the region with the United States.

Diplomatic tension between the United States and Venezuela and Bolivia peaked earlier this month after Chavez and Morales expelled the US ambassadors to the their countries. Washington reciprocated the expulsions.

Bush has sought the free trade agreement, signed with Uribe in 2006, as key to US policy in South America and to build support for Uribe, whose government receives billions annually in US aid to fight violent FARC rebels believed responsible for drug trafficking.

Washington has accused Chavez's government of aiding FARC, a communist group which stands for the Revolutionary Armed Forces of Colombia and has been waging a bloody civil war for decades.

Congressional Democrats have blocked a vote on the free trade accord, arguing it does not provide sufficient measures to protect Colombian labour unions and the environment, and harms US workers.

Uribe said the free trade agreement is crucial to providing better jobs in his country, to improve the economy and access to health care and better education.

"It is very important ... from and economic standpoint," Uribe said, adding the agreement greatly increases Colombia's opportunity to attract foreign investment.

Bush and Uribe also touted recent successes against FARC, including the rescue of 15 FARC-held hostages in July. Three American contractors were among those rescued, along with former Colombian presidential candidate Ingrid Betancourt, who held been held for years.

The rescue was a major symbolic blow to the once powerful outfit, which has significantly dwindled in size in recent years following an aggressive campaign by the Colombian miliary and the defections of hundreds of militants.

"FARC is weaker," Bush said. "FARC is on the run." (dpa)