Leopoldo Lopez and Antonio Ledezma were arrested by armed security agents for violating the terms of their house arrest.
Venezuela: Two opposition leaders arrested as crisis worsens
Two of Venezuela's top opposition leaders were arrested by armed security agents in the middle of the night on Tuesday as the crisis in the South American country worsens.
Leopoldo Lopez and Antonio Ledezma were taken to Ramo Verde military prison, which is south of Caracas, having been previously put under house arrest.
The arrests occurred two days after Venezuela chose members for a constituent assembly, a controversial election which the opposition boycotted.
Initial reports said as many as 10 more people were killed on Sunday alone after several months of growing anti-government protests in Venezuela's capital and elsewhere. Violent clashes have already claimed 120 lives over an election that would effectively re-write the country's current constitution.
Mr Lopez and Mr Ledezma were accused by the Supreme Court, which is allied with President Nicolas Maduro's government, of violating terms of their house arrest.
Both men's allies deny the charges and released a video Mr Lopez filmed last week saying that he expected to be sent to prison again soon.
"If you are looking at this video now, it's precisely because that occurred, because they came and they illegally imprisoned me again unjustly, a prisoner of consciousness, a prisoner for my ideas, a prisoner for wanting a better Venezuela," Mr Lopez said.
In the wake of the arrests, the UN Secretary General Antonio Guterres said it was concerned that the escalation of political tensions would make it difficult to find a peaceful solution to the crisis.
While the United States, which has already imposed financial sanctions on President Maduro, described Mr Lopez and Mr Ledezma's incarceration as "very alarming".