The new bloc would be an alternative to the Organisation of American States (OAS), the main forum for regional affairs in the past 50 years.
Mexico has been hosting a regional summit in the beach resort of Cancun.
The OAS has been dogged by rifts between some members and the US over economic policy and trade, and criticised for promoting US interests.
The proposed new grouping was one of the main issues on the agenda of the two-day summit, which ended on Tuesday.
It "must as a priority push for regional integration... and promote the regional agenda in global meetings", Mexican President Felipe Calderon told the summit, which includes leaders and representatives from 32 countries.
It's very important that we don't try to replace the OAS. The OAS is a permanent organisation that has its own functions
Chilean President-elect Sebastian Pinera
Argentina wins Falklands backing
Cuban President Raul Castro was quick to applaud Mr Calderon's announcement as a historic move toward "the constitution of a purely Latin American and Caribbean regional organisation".
Cuba was suspended from the OAS in 1962 because of its socialist political system. In 2009, the OAS voted to lift Cuba's suspension but the country has declined to rejoin.
Venezuelan President Hugo Chavez earlier expressed his support for the proposal, citing it as a move away from US "colonising" of the region.
A US State Department official, Arturo Valenzuela, said he did not see the new body as a problem.
"This should not be an effort that would replace the OAS, " he said.
The terms of the new bloc and whether it would replace the Rio Group of Latin American countries has not been clarified.
"It's very important that we don't try to replace the OAS," said Chile's President-elect Sebastian Pinera. "The OAS is a permanent organisation that has its own functions."
On Monday, Bolivian President Evo Morales proposed that it begin operating in July 2011 with a summit hosted by Venezuela.
The Cancun summit has also unanimously backed Argentina's claim over the British-owned Falklands.
Argentina is angered that a UK firm has begun drilling for oil off the Falkland Islands, which lie about 450km (280 miles) off the Argentine coast.
Argentina and Britain went to war over the South Atlantic islands, which Argentina calls the Malvinas, in 1982, after Buenos Aires invaded them.
The leaders at Cancun also discussed whether to recognise Porfirio Lobo as the legitimate president of Honduras after he was elected president under interim authorities following a 28 June coup that ousted Manuel Zelaya.
A long-term plan to help Haiti recover from the devastating January earthquake was also on the agenda.
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