The Unitary Platform (PUD) said it was able to inscribe ex-diplomat Edmundo González after the deadline for registrations was extended.

The PUD said Mr González was its "provisional" candidate, hinting that he may be replaced before the election.

Whoever is chosen will take on current President Nicolás Maduro.

The PUD had originally backed María Corina Machado as its candidate to unseat Mr Maduro, who has been in power since 2013.

Ms Machado won an opposition primary held in October with more than 90% of the votes and had succeeded in uniting the notoriously divided opposition groups.

But since then, she has had a ban which prevents her from running for public office confirmed by the Supreme Court, which is stacked with government loyalists.

President Maduro, who has been in power since 2013, has withstood international pressure to lift the ban on Ms Machado.

Nicolás Maduro held a rally after registering his candidacy for a third term

He told his supporters last month that "we're going to win by hook or by crook, we're going to win, always".

With the deadline for the registration of candidates fast approaching and Ms Machado's ban still in place, the PUD on Friday picked Corina Yoris to replace her.

Ms Yoris, an 80-year-old academic, is relatively unknown even in opposition circles. The fact that she is a newcomer to politics was seen as an asset by the coalition, which argued that this made it harder for her opponents to discredit her.

But when it came to registering her candidacy by the deadline set for Monday evening, however, the opposition coalition hit a wall.

In videos uploaded to social media, the PUD showed how they repeatedly tried and failed to log into the electoral council website to register Ms Yoris's candidacy.

One of the parties which forms part of the coalition, however, was granted an extension and was able to log into the system to register Mr González.

A variety of other parties were also able to file candidates bringing the total number of presidential candidates to 13, but some of them are aligned to the government and are not thought to be serious challengers to President Maduro.

The PUD said in a statement that the candidacy of Mr González was "provisional... given the clear impossibility of registering the chosen candidate so far", suggesting the former diplomat was chosen as a placeholder.

Parties can make changes to their presidential ticket until 20 April and the opposition coalition is expected to replace him with a unity candidate.

Another politician who was successful in registering, Manuel Rosales, has already announced that he would be willing to give up his place on the ballot in favour of a unity candidate.