Mendez said he was disappointed that Bahrain postponed his scheduled May visit to the country to investigate the rights situation there. The government said a national dialogue was taking longer than expected and his visit might undermine chances for reconciliation.
"The government is facing many challenges in light of the on-going tensions in Bahrain," Mendez said in a statement. "I would have conducted my visit in the spirit of cooperation and expected the government to share that approach; regrettably, this does not appear to be the case."
Bahrain was criticized for taking a heavy hand in its response to a 2011 uprising. The government said it's committed to reforms outlined by an independent panel of inquiry investigating the response.
Mendez said the government's delay, its second, follows a week of clashes between demonstrators and security forces. Several reports released ahead of last weekend's Formula 1 race in Bahrain accused the government of torturing opponents.
Mendez said he was frustrated that no alternative dates were proposed.
"I can understand that this postponement could be perceived as if there is something to hide," he said.