Guaido had risked arrest on his return to Venezuela for flouting a court-imposed travel ban to visit other Latin American countries.
Mr Guaido denounces Mr Maduro as a scammer whose re-election previous year was fraudulent, and says his regime is to blame for an economic meltdown that has led to widespread food and medicine shortages and hyperinflation.
The International Monetary Fund (IMF) has not made a decision on recognizing a new government in Venezuela, the organisation's spokesperson said on Thursday.
Venezuelan opposition leader and self-declared acting president Juan Guaido speaks to supporters during a rally to bring pressure to the military to allow in USA humanitarian aid, in eastern Caracas on 12 February 2019.
The Venezuelan government did not say why he was being held and did not respond to calls seeking comment.
Germany's Foreign Minister Heiko Maas on Wednesday slammed the expulsion of Mr Kriener as "incomprehensible", and said Berlin and its European partners would continue to back Mr Guaido.
His supporters say his re-election was legal and have accused Mr Guaido of violating the constitution.More news: Canadian PM Trudeau's former top aide testifies in his defence
Guaido also said Maduro had effectively been ignoring him since his return to Venezuela in hopes that his political momentum will fade. On Tuesday, Maduro belittled his opponents as "opportunists and cowards", but did not mention Guaido by name.
On Wednesday, the government of Venezuelan President Nicolas Maduro announced it was giving Kriener 48 hours to leave the country, a move seen as a response to Germany's support for Guaido.
Venezuelan leader Nicolas Maduro has cut ties with Colombia after opposition leaders used the neighboring Andean nation as a launching point for humanitarian aid meant to undermine his authority.
White House national security adviser John Bolton announced that the USA was "putting foreign financial institutions on notice that they will face sanctions for being involved in facilitating illegitimate transactions that benefit Nicolas Maduro and his corrupt network". The guard said the security forces wore jackets indicating that they were from the military intelligence service.More news: Brie Larson: Captain Marvel could be 'biggest feminist movie of all time'
The US is already trying to cripple Maduro's access to finances via sanctions on state oil company PDVSA and handing control to Guaido of Venezuelan bank accounts in the United States. Kriener and other diplomats greeted opposition leader Juan Guaido when he returned to Venezuela on Monday and vowed to intensify his campaign to topple the Maduro government.
Phil Gunson, a political consultant at the International Crisis Group, suggested on Twitter that the incident could strain already tense relations between the United States and Venezuela.More news: Indiana Basketball keeps hopes of making NCAA Tournament alive