The presidential gathering in Cochabamba, Bolivia - where Morales began his political career as the leader of coca leaf farmers - is aimed at expressing outrage over his "virtual kidnapping" and the U.S. pressure they believe spurred it.
"Latin America has to react," Ecuadorean President Rafael Correa said before departing for Bolivia. "Imagine for one second if this had happened with a European president or the U.S. president - it probably would've been grounds for war. And here they think they can infringe and crush international law."
Despite the rhetoric, no Latin American country has offered asylum yet to Snowden, who is wanted by Washington for disclosure of intelligence secrets. Two radical leftist governments - Venezuela and Cuba - are in a cautious rapprochement with the United States that would be jeopardized if they gave him sanctuary.
Russia is growing impatient over Snowden's stay in a Moscow airport and officials have urged him to leave.
Bolivia said Morales was returning from Moscow on Tuesday when France and Portugal abruptly banned his plane from entering their airspace and it was forced to land in Vienna. Austrian officials said they inspected his plane there, but Bolivia's defense minister denied this.
This unusual treatment of a presidential plane upset leaders in Latin America, which has a history of U.S.-backed coups.
The presidents of Ecuador, Venezuela, Argentina, Uruguay and Suriname will attend Thursday's meeting. More moderate governments in the region will send lower-ranking officials, indicating the 12-nation South American bloc Unasur is split.
Noticeably absent would be presidents from regional heavyweight Brazil and three countries that are close U.S. allies: Peru, Chile and Colombia.
Bolivia and Venezuela said they had received extradition requests for Snowden from the United States, which they repudiated. Bolivia called it "illegal and unfounded" since Morales never even met with Snowden, much less took him aboard.
"While we were flying (home), the U.S. government gave our foreign ministry a scrap of paper asking for the extradition of this young man, Snowden," said Venezuelan PresidentNicolas Maduro, who returned from Russia on Thursday after attending an energy conference with Morales.
"They don't have the moral standing to demand the extradition of a young man who was alerting to the illegality with which the Pentagon, the CIA and the U.S. act," he said.
U.S. State Department spokesman Jen Psaki, when asked about the request made to Bolivia, said: "We've broadly asked for Mr. Snowden to be returned from any country where he may be, where he may land, where he may transit."
To ally the anger of allies over reported U.S. spying that came to light in the Snowden scandal, U.S. President Barack Obama has agreed to talks with the European Union, and also agreed to bilateral talks with Germany after speaking on Wednesday night with ChancellorAngela Merkel. "I made clear spying on institutions within the European Union is not how we would expect those we consider friends to treat us," Merkel said. South America's most outspoken leftist leaders will meet in Bolivia on Thursday to rally behind Bolivian President Evo Morales, whose plane was diverted in...