Venezuela's unified opposition presidential candidate unable to register to run

Venezuela's main opposition parties have been unable to register a candidate backed by them all for this summer's presidential election, raising concerns in the international community over whether the vote will be free and fair.

The ballot is set to take place on July 28. Election authorities say incumbent President Nicolas Maduro and 12 others registered as candidates.

The opposition parties had named 80-year-old university professor Corina Yoris as an alternate unified candidate after Venezuela's supreme court disqualified their first choice, a former lawmaker who calls for economic liberalization, from running. The top court is under the influence of Maduro's leftist administration.

However, Yoris said she was unable to access the system to register her candidacy before a Monday deadline.

Opposition parties say that, under election rules, they have until mid-April to name substitute candidates, but it is not clear whether that will be possible.

The United States and some South American countries have expressed concerns about the blocking of candidates.