Russian news agencies say a shipment of Russian medicine and medical equipment has arrived in Venezuela.

The reports on state news agencies RIA-Novosti and Tass did not give the overall size of the shipment or the specifics of what it contained. RIA-Novosti cited a diplomatic source as saying the aid ship was made under the aegis of the World Health Organization.

Russia is an ally of Venezuelan President Nicolas Maduro, who is under challenge from opposition leader Juan Guaido in a resurgence of the country's political crisis.

Guaido has been rallying international support for his challenge to Maduro and calling for international emergency aid.

Maduro is vowing to block aid from entering Venezuela, saying the effort is part of a U.S.-led coup attempt.