BELGRADE, Serbia — A United States senator expressed hope on Tuesday that Serbia won’t grant diplomatic status to the Russian staff of a controversial facility that some believe is a spy base but that Moscow insists is a disaster relief center.

Wisconsin Republican Ron Johnson, who chairs the U.S. Senate Committee on Homeland Security and Governmental Affairs, said that such a move by Serbia would not be in the Balkan country’s interest and would send a “very bad signal.”

Johnson spoke in Serbia’s capital, Belgrade, after talks with Serbia’s President Aleksandar Vucic. Serbia is seeking European Union membership after years of crisis during the Balkan wars of the 1990s, but also has close ties with Russia.

“I am hoping that President Vucic and Serbia resist any attempt to offer immunity” to the staff of the Russian-Serbian Humanitarian Center, Johnson said. “I think that’d send a very bad signal. It would not surely be in the best interest of the people of Serbia in terms of the western flow of capital to help build your economy.”

Moscow has denied speculation that the Russian-Serbian Humanitarian Center, which opened in 2011 in the southern city Serbian of Nis, is really a station for eavesdropping on Western interests in the Balkans — a tense European region which Russia considers a zone of interest.

The Russian Ministry for Emergency Situations is a partner in the center. The powerful semi-military outfit’s activities do include disaster relief, but the agency also carries out jobs for Russia’s security services. The ministry has long played a role in Serbia, including de-mining and clearing unexploded ordnance from the 1999 NATO bombing of the country.

Johnson said that for Serbia to benefit from an economic infusion from the West, “you need as little corruption as possible and you also need an indication that a country is really leaning toward western democracies and free-market capitalism, and leaning against the type of aggression that unfortunately, Vladimir Putin is demonstrating with Russia currently.”

The U.S. senator insisted that rather than becoming a “friendly rival” of the West after the breakup of the Soviet Union, Russia has turned into an “unfriendly adversary.”

“I think America stands ready for Russia to become that friendly rival, but it’s going to be up to Vladimir Putin and Russia to make that decision,” Johnson said. “I think America, I think the West, has to respond with strength and resolve ourselves so that Vladimir Putin understands that we will stand up to his bullying, to his aggression which is in nobody’s best interest.”

Serbia’s President Vucic was non-committal about his intentions regarding diplomatic status for the Russian staff members of the Russia-Serbia center.

“We are making decisions in accordance with our interests,” Vucic said, adding: “We have not been exposed to any sort of aggression.”