U.S. President Barack Obama and Cuban President Raul Castro broke the ice at the historic Summit of the Americas in Panama on Saturday with a handshake, marking their first encounter since a thawing of relations in December.

Talks between the two leaders are expected to begin Saturday to chart a more cooperative future between the U.S. and Cuba. It is also the first time Cuba will be attending the summit in its 21-year history. United Nations Secretary-General Ban Ki-moon emphasized the importance of Castro's attendance on Saturday.

"The presence here today of President Raul Castro of Cuba embodies a longing expressed by many in the region," Ban said.

As the Associated Press explains, the challenges facing Obama in the negotiations "are huge."

AP continues:

The U.S. embargo on Cuba, which Obama has talked about possibly dismantling as part of the rapprochement, has long been an obstacle to closer ties with Latin America, where mistrust of the U.S. runs deep following a history of support for coups and military dictatorships.

Obama also touted a decision to request from Congress $1 billion in aid for Central America to speed up development that aims to make streets there safer and reduce the flow of migrants to the U.S.

Observers are also anxious to hear whether Washington is ready to remove Cuba from the U.S. list of state sponsors of terrorism. According to Al Jazeera, "In a move that could irritate Cuba, Obama held a closed-door discussion before the summit with dissident lawyer Laritza Diversent and political activist Manuel Cuesta Moura, along with a dozen other activists from the Americas."

And as Democracy Now! reported on Friday, while the U.S. considers friendlier relations with Cuba, it faces new tensions at the summit over its recent sanctions against Venezuela, a close ally of Cuba. Miguel Tinker Salas analyzed the situation:

The stage seems to be set for a repeat. Every regional body that does not include the United States, including the Union of South America (UNASUR) and the Community of Latin American and Caribbean States (CELAC), has condemned the sanctions. The Group of 77, an association of developing countries in the United Nations, has also denounced the measures. Washington sought to isolate Venezuela in Latin America, and it failed.

According to the AP, Venezuelan President Nicolas Maduro took a "symbolic jab" at the U.S. when he arrived in Panama on Saturday by visiting a monument honoring victims of the 1989 U.S. invasion.