MEXICO CITY - After backing Mexico's ongoing battle against drug cartels, President Barack Obama is heading to a Western Hemisphere summit with a sudden spotlight on Cuba.

The president was to fly Friday to the island of Trinidad for the 34-nation Summit of the Americas, a gathering to which Cuba, as the region's only non-democracy, is not invited.

Venezuela President Hugo Chavez, a staunch ally of Cuba's communist government, vowed to torpedo a final summit communique in protest of the country's exclusion.

But Obama's move this week to ease travel and some other restrictions for Cuban-Americans brought an unprecedented reply from Havana. Raul Castro, who took over from his ailing brother, Fidel, a year ago, offered to talk to the Obama administration about all outstanding grievances.

Speaking from a meeting Chavez hosted in Venezuela, Raul Castro declared: "We have sent word to the U.S. government in private and in public that we are willing to discuss everything -- human rights, freedom of the press, political prisoners, everything."

Previously, Cubans had insisted their domestic politics were their own business, and administration officials were trying to determine what to make of the development.

On Tuesday, Obama lifted limits on visits by Americans with relatives in Cuba, eased restrictions on family gifts and cash payments, and moved to allow U.S. telecom companies to expand service to the island.

But the 47-year-old U.S. trade embargo remained in place, despite pleas from U.S. allies that it's counterproductive.

"The embargo has been there long before we were even born," Mexican President Felipe Calderon said. "And yet things have not changed all that much in Cuba."

After talks with Calderon during a pre-summit stop in Mexico, Obama told reporters that further easing depends on Havana sending "signals that they're interested in liberalizing."

He also sounded a note of caution. "A relationship that effectively has been frozen for 50 years is not going to thaw overnight," he said.

Chavez said the summit's final statement and its call for greater democracy reflected American hypocrisy.

"I have no doubt there's more democracy in Cuba," he jeered.

Aides said Obama doesn't plan to meet with Chavez during a summit session, but if the fiery leftist approaches him, Obama would likely engage in polite conversation.

Obama said the gathering, being hosted by the two-island country of Trinidad and Tobago off Venezuela's coast, "offers the opportunity of a new beginning" in the region. And he expected the major focus to be on the global economic crisis, which has America's Latin American neighbors reeling as their prime export markets shut down.

The summit will aim to "jump-start job creation, promote free and fair trade, and develop a coordinated response to this economic crisis," Obama said.

The president's brief stop in Mexico was a chance to talk about trade and immigration with Calderon, but also was a visible show of support for the Mexican's crackdown on drug trafficking. In the two years since it began, more than 10,000 Mexicans have perished as regional cartels target each other and Mexican security forces with contract killings and kidnappings.

Obama lamented the bloodshed, saying it's been "sowing chaos in our communities and robbing so many of a future both here in Mexico and in the United States."

But he said America must do its part to help stop it.

"A demand for drugs in the United States is what is helping to keep these cartels in business," he said. "This war is being waged with guns purchased not here but in the United States."

That said, Obama acknowledged he's unlikely to get Congress to reimpose the Clinton-era ban on assault-style weapons that he favored as a candidate, and which Calderon has urged to help stanch the flow of arms to Mexican drug traffickers.