The left-leaning ALBA regional economic and diplomatic bloc is marking its 10th anniversary in Havana, where it was founded.
Presidents Nicolás Maduro, of Venezuela; Daniel Ortega, of Nicaragua; and Evo Morales, of Bolivia, joined President Raúl Castro of Cuba for festivities on Sunday. Foreign ministers from other bloc-member countries are also attending.
The meeting comes amid tumbling oil prices that are pressuring cash-hungry petroleum exporters like Venezuela.
The Boliviarian Alliance known as ALBA pulls together center-left countries in Latin America and the Caribbean, and places much of its focus on social programs dealing with health, education and other issues.
ALBA aims to counter U.S. influence in the region and was created in 2004 by the late Venezuelan President Hugo Chávez, and Cuban leader Fidel Castro, who has since retired.