Opposition leaders in Venezuela are calling for a rally to protest the surprise arrest of Caracas' mayor.

The arrest of Antonio Ledezma late Thursday has enraged opponents of President Nicolas Maduro and is likely to add to the international condemnation of his government's human rights record. Ledezma is expected to be brought before a judge Friday.

Maduro is facing increasing pressure over Venezuela's mounting economic woes but opposition groups so far have been unable to focus the widespread discontent against his socialist administration.

Venezuela is expected to hold legislative elections later this year which the opposition hopes will give them control of Congress. Recent national polls show Maduro's approval rating has slipped to 22 percent, the lowest of his presidency.