Both men had been under house arrest for prior convictions. The house arrests were revoked, the Venezuelan Supreme Court said, because intelligence officials claimed they were planning to flee in the aftermath of Sunday's controversial elections.
The head of the Organization of American States also blasted Maduro's recent actions, saying he was trying to "silence and subdue an entire people."
OAS Secretary-General Luis Almagro called for new parliamentary elections and accused Maduro's government of killings and repression.
"For the corrupt, the murderers and the torturers, the international community must reply with the greatest severity," he said in a news release.
The detentions come after Venezuelans elected members of a new legislative body in a Sunday vote called for by Maduro and boycotted by the opposition. Virtually all of the new body's members are supporters of the leftist leader.
Critics in Venezuela and outside the restive nation have called the vote a sham.
Some nations have slapped new sanctions
on Venezuela or some of its citizens.
The new body
will have the power to rewrite the Venezuelan Constitution, which Maduro desires, and is expected to replace the previous legislative body, where the opposition has a majority.
The new body will establish a "truth commission" to prosecute political opponents, one of Maduro's top officials said.
Critics say they fear the moves will erase any last traces of democracy in the country. The election came after months of sometimes deadly anti-regime protests and an economic crisis
that led many to leave Venezuela
in search of easier access to food and medicine.
Early morning roundup
Families of the two held opposition leaders distributed separate videos purportedly showing armed men removing the politicians from their homes in the dark of early Tuesday.
Video posted online by Lopez's family shows him being driven away in a car with markings of Venezuela's intelligence service SEBIN.
A different kind of video was posted to the Twitter account of Lopez's wife, one that appears to be a prescient statement about what would happen to him.
In the 6 1/2-minute video reportedly recorded July 17, Lopez sits by his wife and says those who detained him in 2014 could potentially send him back to prison.
"If you are watching this video, then this is precisely what happened, because they came and they unjustly took me as prisoner," he says.
Lopez urges his supporters to continue to work for political change.
"It is worth fighting for Venezuela. Let us not falter in our fight. Let us not give up," he says, adding that he has more motivation because his wife is pregnant.
In another video, a man apparently pulls Ledezma, a former Caracas mayor, out a door early Tuesday.
"He was in pajamas," Ledezma's daughter, Oriette, said in a video statement. "They have kidnapped him once again. We hold the regime responsible for his life and physical integrity."
Who are Lopez and Ledezma?
The Supreme Court said that Lopez and Ledezma had been prohibited from carrying out political actions during their house arrests and that the latter had been forbidden from making declarations to any media.
Both had made public statements in recent days against Sunday's vote.
Lopez, a former mayor of a Caracas district, was put under house arrest
last month, having served the previous couple of years in prison.
Long a vocal opponent of the socialists in power, Lopez was detained in 2014 after at least three people were killed during an anti-government protest in the capital -- violence that authorities blamed on him. His detention was a rallying cry for anti-regime demonstrators.
Lopez was sentenced in 2015 to nearly 14 years in prison, but he was released to house arrest
In a 15-minute video posted online
last week, Lopez urged Venezuelans to keep up anti-regime protests. He called Maduro and his supporters a "very clear threat," saying their goal is to undermine democracy and achieve the "absolute submission of the Venezuelan people."
He was rounded up early Tuesday, his wife, Lilian Tintori, said on social media. Tintori posted video that she says shows her husband being taken away.
"They just took Leopoldo from the house. ... Maduro is responsible if something happens to him," Tintori tweeted.
Lopez, a descendent of South American liberator Simon Bólívar and Venezuela's first president, Cristóbal Mendoza, was banned in 2008 from running for office on accusations of corruption. An international human rights court cleared him in 2011, but the Supreme Court upheld the ban.
Ledezma, known throughout Venezuela for his vocal opposition, was elected Caracas mayor in 2008. He was arrested in February 2015 after Maduro accused him of involvement in a plot to overthrow the government.
In a video posted online Monday
, Ledezma said Sunday's vote "was fraud, plain and simple."
"We know that our public institutions have become instruments of a totalitarian regime, of a tyranny, which decided to continue damaging and destroying our rights," Ledezma said.
His wife, Mitzy Capriles, said her husband was taken to the Ramo Verde Prison. Speaking Tuesday from Madrid, Spain, Capriles said she is "deeply anguished" by her husband's detention and said his attorneys won't be able to speak to him until later Tuesday night.
CNN is unable to confirm the location of either opposition figure.
Attorney general: 'The end of freedom of expression'
Venezuela's attorney general lambasted the election.
"This is the end of freedom of expression, and this freedom has been battered for some time now," Attorney General Luisa Ortega said.
For months, Venezuela has struggled with two interconnected crises: a collapsing economy
and a standoff between Maduro and the opposition.
In December 2015, opposition politicians won a majority of seats in the National Assembly. It seemed like a potential turning point -- the assembly could vote to impeach Maduro, who had verbally clashed with the opposition since he came to power in 2013.
But before lawmakers were sworn into office, Maduro stacked the Supreme Court with his supporters to block any impeachment attempts.
The Supreme Court briefly attempted to dissolve the National Assembly in March, sparking a wave of nearly daily protests. More than 120 people have been killed in the ongoing unrest.
Luis E. Rondón, one of five directors of Venezuela's National Electoral Council, voiced reservations at a news conference about the validity of Sunday's vote.
Normal electoral controls had been relaxed and in some cases eliminated in Sunday's poll, he said. Rondón is the sole director of the electoral council who isn't a supporter of Maduro.
The US Treasury Department slapped sanctions on Maduro
following the vote, calling the election illegitimate and saying that Maduro was disregarding the will of his people. All of the President's assets subject to US jurisdiction were to be frozen. All US citizens are barred from dealing with him, according to the department.
In a nonbinding referendum organized by the opposition in mid-July, an overwhelming majority of voters rejected the planned constituent assembly
. About 7 million Venezuelans voted in that referendum -- 37% of the electorate.
But Maduro's government called the referendum illegal.
Venezuela's national election committee said more than 8 million people cast votes Sunday. The opposition disputes that, and says the number that voted in the July 16 referendum was higher.