Barack Obama, Raul Castro Shake Hands at Historic Summit

US President Barack Obama and Cuba's Raul Castro shook hands and sat near each other Friday at a historic Summit of the Americas, a new milestone in efforts to shed decades of animosity.

Obama and Castro greeted each other as UN chief Ban Ki-moon looked on, before taking their seats with other regional leaders at a Panama City convention center.

The sight of Obama and Castro in the same room instantly became a potent symbol of their bid to renew diplomatic ties that were severed in 1961.

It was the first time that a Cuban leader attended the summit in its 21-year history.

A US official characterized the Obama-Castro greeting as an "informal interaction," adding that "there was not a substantive conversation between the two leaders."

A widely anticipated broader conversation -- the first between US and Cuban leaders since ties broke in 1961 -- is expected on Saturday.

The two leaders briefly shook hands once before, at Nelson Mandela's memorial service in Johannesburg in 2013.

"This summit in Panama has such a special dimension," Organization of American States secretary general Jose Miguel Insulza told the gathering, noting it was the first time all 35 nations were represented.

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

All the regional leaders then headed to a private dinner.

'New chapter'

Senior Obama aide Ben Rhodes said the extent of Saturday's Obama-Castro meeting had yet to be decided, but that they will "take stock" of the negotiations to reopen embassies and discuss lingering "differences."

Rhodes said Obama and Castro had already discussed the ongoing negotiations and the summit by telephone Wednesday -- their second phone call since December, when they announced that the United States and Cuba would move to normalize relations.

But in a move that could irritate Havana, 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.

While declaring that the days of US meddling in the region were over, Obama promised civil society representatives that "the United States will stand up alongside you every step of the way."

Turning to Cuba, Obama said that even as "a new chapter" in relations was launched, "we'll have our differences, government to government, with Cuba on many issues."

Cuban government supporters confronted dissidents on the sidelines of the summit.

For his part, Castro held talks with the president of the US chamber of commerce, Tom Donohue, putting together the leader of the only communist regime in the Americas with a major figure of capitalism.

No terror list decision

The US and Cuban foreign ministers, John Kerry and Bruno Rodriguez, made history themselves late Thursday when they held the highest level talks since 1958, which both sides hailed as "constructive."

But Rhodes said there was no decision yet on one of the key obstacles in diplomatic negotiations, Cuba's presence on the US blacklist of state sponsors of terror.

"I'm not ruling out any announcement but... we are not there yet in terms of a final recommendation being made to the president, and the president making a determination," Rhodes said.

Cuba's presence on the blacklist -- which also includes Iran, Sudan and Syria -- has been a major sticking point in the negotiations.

Once Obama makes a decision, Congress has 45 days to decide whether to override his recommendation.

Venezuela question

Opinion polls show the reconciliation is backed by majorities of Americans and Cubans, though some US lawmakers have been very critical.

And even as Obama moves to remove an old source of tension in US relations with Latin America, he has angered Venezuela over sanctions against officials over an opposition crackdown.

Venezuelan President Nicolas Maduro, Havana's main ally in the region, vowed to bring a petition with 13.4 million signatures urging Obama to lift the sanctions.

Maduro received a hero's welcome at a rally with hundreds of supporters at Panama City's El Chorillo monument, built for victims of the 1989 US military invasion to oust Manuel Noriega.

"The United States must ask forgiveness from Panama and Latin America for the invasion," Maduro thundered, vowing to hand Obama a letter from victims.

But Washington is seeking to ease tensions, dispatching a senior official this week to meet Maduro in Caracas.