The United Nations' top human rights official is visiting Venezuela amid heightened international pressure on President Nicolás Maduro.

U.N. High Commissioner for Human Rights Michelle Bachelet is expected to arrive Wednesday to meet with Maduro and opposition leader Juan Guaidó on a three-day visit.

It's the first trip to the South American country by the head of the U.N. watchdog and is seen as a minor triumph for human rights activists.

But José Miguel Vivanco of Human Rights Watch urged Bachelet to insist on gaining access to a prison where lawmakers are being held and a children's hospital in Caracas.

Vivanco warned Bachelet's visit will be a disappointment if she just meets with officials, opposition leaders and civil society representatives.

He said: "She can do that via Skype from Geneva."