CARACAS (Reuters) - Venezuela arrested 15 senior military officials around the time President Nicolas Maduro won re-election in a widely criticized vote, a rights group said, adding to scores already detained on accusations of conspiring or deserting.

The officials, 14 of whom are high-ranking lieutenants and colonels, were arrested between May 17 and 21, just before and after Sunday’s vote, according to the Penal Forum group. The arrests occurred after authorities investigated government suspicions of a conspiracy, the group said on Thursday.

Maduro, speaking later at a military parade to celebrate his second term, called for the military to remain loyal and said the leader of the purported conspiracy had been captured.

“Are the armed forces going to betray the Venezuelan people?” he said before hundreds of soldiers. “I demand utmost loyalty from the armed forces, utmost loyalty to the constitution.”

The Defense Ministry has not given any details on arrests.

Nine of the officials appeared before a Caracas court on Monday and were charged with military rebellion, treason, mutiny and crimes against military decorum, Penal Forum head Alfredo Romero said. The other six will appear before the court at an unknown later date.

At least three civilians, including one of the officials’ partners, were also arrested, Romero said in a phone interview.

Private lawyers have not been allowed to visit the officials at the hilltop Ramo Verde military prison outside Caracas, Romero said.

Penal Forum has denounced the existence of 373 “political prisoners” in total in Venezuela.

The Maduro government denies that there are “political prisoners,” saying all politicians and members of the security forces in detention are there on legitimate criminal charges, including coup-plotting.

Internal military documents show arrests have been rising sharply within the armed forces, where there is discontent within the ranks, especially at food shortages and dwindling salaries due to Venezuela’s crushing economic crisis.

Documents reviewed by Reuters showed the number of new detentions of soldiers for treason, rebellion and desertion rose to 172 in the first four months of 2018, up three-and-a-half times from the same period of 2017.

Sunday’s vote was slammed by Maduro’s foes and a raft of foreign nations as a farce that did not meet democratic norms.

Maduro, a 55-year-old former bus driver who succeeded Hugo Chavez in 2013, says he is the victim of a U.S.-led conspiracy to topple him and take over Venezuela’s oil reserves.