The mayor said there were better ways of benefiting Londoners
Boris Johnson will not renew an oil deal with Venezuela which provides cheap fuel for London's buses once the agreement ends later this year.
The mayor of London said half-price bus and tram fares for 250,000 Londoners on income support, which were also funded by the deal, would still be honoured.
Mr Johnson said he thought many Londoners were uncomfortable with how the scheme was funded.
Former mayor Ken Livingstone signed the deal at City Hall in February 2007.
In return, a team of officials from the Greater London Authority agreed to work in Venezuela advising on recycling, waste management, traffic and on reducing carbon emissions.
Mr Johnson said: "I think many Londoners felt uncomfortable about the bus operation of one of the world's financial powerhouses being funded by the people of a country where many people live in extreme poverty.
"I simply think there are better ways of benefiting Londoners and better ways of benefiting Venezuelans."
He added: "We will continue to offer the half-priced travel concession to Londoners on income support for the duration for which the deal was originally planned, and will continue to improve the capital's transport system and ensure that it is accessible and able to meet the needs of all those who rely on it."
The current deal is due to conclude on 20 August.
Mr Johnson also said the office set up in Caracas to oversee the deal would be closed, saving an estimated £67,000 per year in running and staff costs.
Mr Livingstone attacked the decision not to renew the deal and close the Venezuelan office.
He said: "It shows that he is more interested in pursuing his right-wing ideological agenda than improving the living standards of the most deprived people in the capital.
"The fact that the first significant action by Johnson's Tory regime is against the poorest people in the capital is highly significant as is the cowardly way he has made the announcement on bank holiday Sunday without any consultation with the organisations representing the thousands of carers, single parents and others affected."
Mr Livingstone added: "The suggestion that Johnson is motivated by any concern about the people of Venezuela is just a lie shown by the fact that he is withdrawing all technical support and advice provided by London under this agreement."
Venezuela has the largest oil reserves in the Americas and its socialist president is the Bush administration's fiercest critic in Latin America.
But in November 2005, it signed a deal with the US state of Massachusetts to provide cheap heating oil to poor households. Similar deals were also signed in Boston and New York.