US Secretary of State Condoleezza Rice has highlighted the importance of democracy in Latin America at the start of a five-day tour of the region.
Ms Rice held talks with Brazil's President Lula
Speaking in Brazil, Ms Rice said Latin American countries should keep faith with democratic reforms.
She criticised Cuba for refusing to accept reform, and voiced concerns about Venezuelan President Hugo Chavez.
After leaving Brazil, Ms Rice was due to visit Colombia for talks, followed by stops in Chile and El Salvador.
Her comments came a week after the removal from office of the elected president of Ecuador, Lucio Gutierrez.
Washington, which has yet to recognise the new government in Quito, has urged its members to respect the rule of law.
Mr Gutierrez, who was replaced by his vice-president, is now in exile in Brazil.
Speaking in Brazil's capital, Brasilia, Ms Rice told a 400-strong audience that democracy would eventually help ease the deep poverty that affects much of Latin America.
"In time the blessings of democracy come to everyone who keeps the faith with the principles of democracy," she said.
She criticised Cuba's leaders, talking of an "empty place" at the Organisation of American States because of a lack or democratic reforms.
"Our job has to be as members of this hemisphere to pursue policies that give democracy a chance not just to hold elections but to then actually provide for its people," Ms Rice said.
She said that US economic policies promoting free trade must be tied to human development to bolster the region's democracies.
Earlier, Ms Rice hailed Brazil's growing influence in the region as an emerging power.
"Brazil is a regional power and, in fact, Brazil is a growing global presence, and we think that's a good thing," she was quoted as saying by the AFP news agency.
Appeals for support
The BBC's Brazil correspondent, Steve Kingstone, says the US secretary of state's visit is seen as a test of relations between Washington and its key regional partner.
The US wants support from Brazil in containing Venezuela's left-wing President, Hugo Chavez, whom it describes as a destabilising influence.
CONDOLEEZZA RICE ITINERARY
First tour of region since taking up post in January 2005
Tour follows visits to Europe in February and Asia in March
Likely issues: Ecuador's political crisis, Venezuela, deadlock over new head of Organization of American States
For its part, Brazil is seeking US support for its bid to obtain a permanent seat on the United Nations Security Council, our correspondent says.
Commentators say the Latin American trip aims to revive relations overshadowed in recent years by the war on terror and conflicts in Iraq and Afghanistan.
More than half of South America's population is now ruled by left-leaning presidents, all elected in the last six years and seeking to distance themselves from Washington.
Over the past two decades Latin America has turned to democracy and many governments have followed Washington's formula for economic liberalisation.
But 100 million people there live on less than $1 a day and the region has the most unequal distribution of wealth in the world.