By Andrew Cawthorne and Mario Naranjo
CARACAS (Reuters) - Venezuela's President Hugo Chavez has not been seen or heard in public since returning a week ago from his latest cancer treatment in Cuba but was well enough to monitor a jail riot in Caracas, an ally said on Friday.
The usually garrulous and attention-seeking Chavez's disappearances from public view have become longer and more frequent this year. That has fueled speculation his condition has worsened and may complicate a re-election bid in October.
Allies in the ruling Socialist Party, however, insist Chavez, 57, remains on top of government affairs, is recovering and is not mulling a succession.
"The 'comandante' has been in constant communication with us, he calls all the time," Diosdado Cabello, head of the National Assembly and a leader of the Socialist Party, told reporters outside La Planta prison in Caracas, where troops quelled a riot on Thursday.
"The president has been tracking what's been going on here ... His eye is constantly on (state broadcaster) VTV, checking what's happening."
Chavez has been seen only twice in public since mid-April. That included a half-hour appearance last Friday when he returned from Cuba after completing radiotherapy sessions.
Despite rumors he was wheelchair-bound, Chavez walked without help down the airplane stairs and then inspected a military guard of honor. He spoke with a firm voice and even sang a song in honor of Venezuela's mothers.
Since then, Chavez has again gone to ground, presumably under strict doctor's orders in his presidential palace.
Even on Twitter, where he is usually prolific and has a following of nearly 3 million people, Chavez has been silent since Sunday when he sent greetings for Mother's Day and celebrated a Venezuelan driver's Formula One victory.
The official line is that he is recovering from tough treatment and will soon be launching his campaign for the October 7 election in which he is being challenged by state governor Henrique Capriles.
Chavez wrongly claimed to be "completely cured" at the end of 2011 so many Venezuelans are skeptical about his condition, especially given the plethora of rumors and leaks from pro-opposition media citing medical sources.
With the details of his health a state secret, all that is officially known is that Chavez has had three operations and two malignant tumors removed from his pelvic area.
The second one was removed after what he called a recurrence of cancer this year.
The implications of a downturn in his health are enormous less than five months away from an election, where Chavez wants to extend his 13-year rule of the OPEC member.
The wider region also is watching closely - nowhere more so than in communist-run Cuba, which depends on subsidized Venezuelan oil to keep its economy afloat.
U.S. President Barack Obama's government is staying largely quiet about Chavez but is highly interested in the fate of a man who has been Washington's main critic in the region yet has also kept oil exports flowing north.
(Editing by Bill Trott)