(CNN) -- Venezuelan President Hugo Chavez arrived in Havana early Wednesday for a new round of medical treatment, Cuban state media reported.
The timing of his departure, weeks before regional elections in Venezuela, has fueled renewed speculation about the president's health.
It was unclear how long Chavez, who declared himself cancer-free in July, would remain in Cuba.
"Nobody should be alarmed. Nobody should worry. This is part of the treatment that the comandante has been following," said Diosdado Cabello, president of Venezuela's National Assembly and a close Chavez ally.
Chavez will undergo several sessions of hyperbaric oxygen therapy, state media said.
The treatment helps prevent and mend bone damage caused by radiation therapy, according to the American Cancer Society. It involves breathing pure oxygen in a sealed chamber that has been pressurized at up to three times normal atmospheric pressure.
Chavez underwent several rounds of radiation therapy in Havana earlier this year. The Venezuelan president repeatedly spoke publicly about his cancer battle, but he never specified what type of cancer doctors were treating.
Members of Venezuela's opposition wished Chavez good health but criticized him Wednesday for a lack of transparency regarding his health and treatment.
"I think that he should speak to the Venezuelan people with transparency about what the situation is, what the scope of this treatment is," said Henrique Capriles Radonski, who faced off against Chavez in October's presidential election and is now vying for governor in Venezuela's Miranda state. "This is how it should be in Venezuela, and you can see that it's like this in other countries."
Cabello defended Chavez and said such criticism was unwarranted.
"The president has been very clear with the Venezuelan people about the illness he has and how it has been treated," he said.
Health rumors dogged Chavez on the campaign trail this year, but didn't stop him from winning re-election in October.
From June 2011 to May 2012, he underwent cancer treatment in Cuba, raising speculation about his political future and about a possible successor, especially when he named 10 people to his inner circle of advisers, known as the Council of State.
But Chavez declared himself cancer-free in July and went ahead with his campaign.
Details of his health, however, have been a closely held secret, and some people who claim to have insider knowledge say the president is in much worse condition than he publicly lets on.
The National Assembly on Tuesday voted to grant Chavez permission to travel to Cuba for the treatment, the state-run AVN news agency reported.
Word of Chavez's trip to Cuba sparked debate on the streets of Caracas, the capital.
Chavez used to appear much more frequently on national television, said Hedbert Cortes, a worker.
"Before he would talk on TV for hours. Now he's on less. I think this is because of his health," Cortes said.
Andres Berroteran said he was hoping for the best for Chavez.
"That everything turns out well and he recuperates," the insurance analyst said. "Like any human being, we wish him the best."
Journalist Osmary Hernandez and CNN's Patrick Oppmann, Claudia Dominguez and Nelson Quinones contributed to this report