Venezuelan President Hugo Chavez has pledged to defend Iran from attack as the summit of the Non-Aligned Movement gets under way in Havana, Cuba.
President Chavez is an outspoken critic of US policy
He told Iranian President Mahmoud Ahmedinejad "under any scenario, we are with you just like we are with Cuba".
The summit brings together 118 nations, including many developing countries, for an alternative forum of debate.
It was unclear whether Fidel Castro - who has appeared in a new video as he convalesces - would attend the summit.
In the latest of several videos broadcast on Cuban state TV since the veteran leader fell ill some six weeks ago, a gaunt-looking Mr Castro briefly stands as he greets close ally Mr Chavez.
"[Fidel] is walking, singing, he even sang a song... I saw him well enough to play baseball again, almost," Mr Chavez told reporters from the conference, according to Reuters news agency.
Fidel's younger brother, Raul, who has taken over the president's duties for the period of his illness, has been making his first public appearances at the summit.
'Blood will run'
Mr Chavez said he would defend Iran which he said was "under threat" of invasion, after it ignored UN demands to suspend uranium enrichment.
Iran denies it is seeking to develop a nuclear weapon.
"We are with you just like we are with Cuba," Mr Chavez said.
"If the United States invades Cuba, blood will run."
The BBC's Stephen Gibbs, in Havana, says the huge cast list of dignitaries who have arrived in Havana for the two-day summit includes some of Washington's least favourite world leaders.
Along with Mr Chavez, the presidents of Iran and Belarus hope that the Non-Aligned Movement can become a powerful alternative to what they see as US attempts at world dominance.
But others take a more moderate stand.
The Indian and Pakistani delegations are among several that would rather see the group concentrate on just being a voice for the developing and developed world.
There are a broad array of topics up for discussion, but high on the agenda are violence in the Middle East and nuclear proliferation.
The summit's final declaration will contain quite explicit criticism of American foreign policy, say correspondents.
The US declined an invitation to attend and says it will not comment on proceedings. Some dismiss the NAM as a throwback to the Cold War.
The summit comes a week before the UN General Assembly in New York next week, and from Havana Mr Chavez also accused the US of deliberately trying to prevent him from attending.
He said the Americans had refused to grant entry visas to his personal doctors - including six Cubans - and members of his security team.
The US confirmed visas had not been issued, but said the Venezuelan government had been very late in applying.
But Mr Chavez said he would get to New York somehow - "even if it's on horseback".