An anti-government demonstrator cries during a vigil in honor of those who have been killed during clashes between security forces and demonstrators in Caracas, on Monday.
In a statement, the Supreme Court said protest leader Leopoldo Lopez and Caracas mayor Antonio Ledezma were sent back to prison because they had violated the terms of their house arrest by making political statements.
Both men's allies denied the charges and vowed to continue to try to push the ruling party from power.
Latin American nations including Chile, Colombia, Mexico and Peru joined the USA in saying they did not recognize the results of Sunday's election, while Brazil, Costa Rica and Panama joined the condemnation of Lopez and Ledezma's arrest.
"Mr Lopez and Mr Ledezma are political prisoners being held illegally by the regime", Trump said.
He was rounded up early Tuesday, his wife, Lilian Tintori, said on social media. Lopez had been held more than three years in a military jail until last month, when he was unexpectedly released in what was seen as a potential breakthrough in the country's political standoff. The couple had been allowed some conjugal visits. In addition to rewriting the constitution, the legislative superbody will have the power to dissolve the opposition-led congress, eliminating any institutional check on Maduro's powers.
Lopez and Ledezma are among Maduro's most vocal and influential critics.
President Maduro has declared victory in Sunday's elections for the new body, which could replace the current National Assembly.
The arrests occurred two days after Venezuela chose members for a constituent assembly, a controversial election which the opposition boycotted. He didn't give a specific time.
As fears over civil unrest and instability in the country grew on Tuesday, the Foreign Office said it had withdrawn the families of its embassy staff and instructed Britons that they should consider leaving too.
The two were under house arrest for previous opposition activities. A woman in the video can be heard screaming, "They're taking Ledezma, they're taking Ledezma, dictatorship!"
A video posted showed him being taken away by members of the Venezuelan intelligence service, Sebin.
They were under house arrest after accusations of inciting violence during anti-government protests in 2014, the BBC reported. Among other measures, he said he would use the assembly's powers to bar opposition candidates from running in gubernatorial elections in December unless they sit with his party to negotiate an end to hostilities that have generated four months of protests that have killed at least 120 and wounded almost 2,000.
However, imposing sanctions on a head of state is rare and can be symbolically powerful, leading other countries to similarly shun such a leader.
Venezuela's national election committee said more than 8 million people cast votes Sunday.
The Atlanta-based Carter Center whose founder, former U.S. President Jimmy Carter, once said Venezuela had one of the best election processes in the world, also came out against the process.
The vote was marred by deadly protests, adding to a death toll of 125 in the past four months in demonstrations against Maduro and against the assembly.
Later, the White House issued a statement condemning "the Maduro dictatorship" over the arrests and saying Lopez and Ledezma are political prisoners. "The United States holds Maduro ... personally responsible for the health and safety of Mr. Lopez, Mr. Ledezma, and any others seized".
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 hard to find a peaceful solution to the crisis.
The French, British, Spanish and Mexican ambassadors to Venezuela visited the opposition-controlled National Assembly on Tuesday and met with legislators as a show of support.