MOSCOW/CARACAS –

A group of Russian military specialists has arrived in the Venezuelan capital of Caracas, the Interfax news agency reported on Wednesday, as Venezuelan President Nicolas Maduro meets with his Russian counterpart, Vladimir Putin, to improve cooperation.

Moscow has been one of Maduro's biggest backers amid what it has described as U.S. efforts to undermine him, and has provided loans and other help for the military and oil industry in Venezuela, where Russia has major energy investments.

The Russian government has dispatched troops to Venezuela several times already this year to service military equipment, despite the U.S. government repeatedly warning Putin against sending Maduro military assistance.

The Interfax report did not say how many specialists had been sent, but it cited an unnamed source saying they had been dispatched to carry out maintenance on Russian military hardware sold to the Latin American country.

Two Russian planes had landed recently in Venezuela, Interfax reported, citing social media reports.

A Reuters photographer on Wednesday saw one Russian air force jet at Caracas' main Maiquetia airport. The plane had left Moscow on Sept 20, according to flight tracking website Flight Radar.

Maduro on Monday left for a state visit to Russia and on Wednesday met with Putin, who said he backed negotiations between Venezuela's government and the opposition.

Venezuelan opposition leader Juan Guaido said earlier this month that negotiations in Barbados with the government, mediated by Norway, had been exhausted after the Maduro administration withdrew delegates following a tightening of U.S. sanctions. A small group of opposition lawmakers has entered separate talks with Maduro, which Guaido has rejected.

Meeting Maduro in Moscow, Putin said Moscow considered any refusal to hold dialogue to be "irrational and harmful for the country and a threat to the welfare of the population."