Cuban President Raul Castro spent Sunday in private meetings with socialist ally Hugo Chavez after a warm public salute to the Venezuelan president for helping Cuba through difficult times.

Castro and Chavez were not scheduled to appear in public the day after they agreed to joint projects worth more than $2 billion.

Chavez — a longtime ally of Fidel Castro who says he is building "21st-century socialism" in his oil-rich South American nation — has given Fidel's younger brother a warm welcome and praised him for challenging U.S. "imperialism" for decades.

Castro, in turn, thanked Venezuela for increasing cooperation with the communist-led island.

"In the name of Cuba, we thank you for your solidarity with the Cuban Revolution," said the 77-year-old Castro. "We've been able to leave the difficult years behind."

Fidel Castro signed Cuba's first cooperation agreement with Venezuela eight years ago.

Raul Castro stopped first in Venezuela on his first foreign trip as president, a testament to Cuba's reliance on the South American nation that provides the island with oil at a discount.

Venezuela sells Cuba about 90,000 barrels of crude oil per day on preferential terms, and hopes to increase shipments to 150,000 barrels per day by 2013.

Venezuela also is the fifth-largest exporter of oil to the U.S. Washington's nearly 50-year-old trade embargo against Cuba prohibits nearly all U.S. commerce with the island.

Plunging world oil prices are raising doubts about the future of Venezuela's international largess. But Venezuela and Cuba forged ahead Saturday with plans to expand Cuba's oil refineries.

The Cuban government, meanwhile, has sent Venezuela 30,000 Cuban doctors, nurses, sports trainers and agricultural technicians.

Castro replaced his 82-year-old brother Fidel as Cuba's president in February. He offered Chavez and the Venezuelan people "a hug" from Fidel, who has not been seen in public since undergoing emergency intestinal surgery in July 2006.

Castro said he hopes voters approve a proposed constitutional amendment to lift limits on presidential elections and allow Chavez to run for re-election in 2012. Venezuelan election officials say the term-limits referendum could be held in March.