MOSCOW— Most European Union leaders seeking to diffuse the tensions between Russia and Ukraine have been traveling to Kyiv and Washington. But Prime Minister Viktor Orban of Hungary is visiting Moscow on Tuesday to meet with President Vladimir V. Putin, in a visit that opposition parties have denounced as “treasonous.”
Mr. Orban, perhaps the Kremlin’s closest ally inside the European Union, has long been accused of undermining the 27-member bloc’s common foreign policy when it comes to priorities like Russia, Ukraine and China.
“Mr. Orban is practically behaving like a tool of Russian foreign policy,” said Peter Kreko, a senior fellow at the Center for European Policy Analysis and director of Political Capital, a research group in Budapest.
Relations between Kyiv and Budapest soured over a 2017 language law that Hungary said discriminated against the ethnic Hungarian minority in the country’s west. Since then, Budapest has blocked operations of the NATO-Ukraine Council, the primary forum for the military alliance to engage with Kyiv.
But critics say Mr. Orban was carrying water for Mr. Putin long before. After Russia annexed Ukraine’s Crimean peninsula in 2015, Mr. Orban opposed the imposition of E.U. sanctions, though Hungary eventually signed onto them.
The Ukraine crisis has heightened calls for the European Union, which collectively sources 40 percent of its natural gas from Russia, to diversify its energy supply. Yet Mr. Orban has done the opposite: He signed a 15-year-deal with Gazprom for gas supplies in September. On Friday, he said he would seek to significantly increase the gas supplied by Russia to Hungary.
The new contract was seen as undermining Kyiv, because the delivery route would bypass Ukraine’s pipelines.
Hungary has also demurred on the question of increasing the presence of NATO troops on its territory, unlike other European countries that were behind the Iron Curtain during the Cold War. The foreign ministry in Budapest signaled last week that it would not host further NATO troops and said that it would not increase aid to Ukraine.
Budapest did not object to the deployment of NATO troops in Ukraine’s neighborhood, said Defense Minister Tibor Benko, but he said that Hungary should “perform this task on its own.”
Mr. Orban declined to criticize Russia in a radio appearance on Friday, saying that his priority for his trip to Moscow was “a balanced economic relationship.”
Mr. Orban’s policy stands in contrast to public opinion in his country. NATO is the most popular international organization in the country, according to a poll last year from the GLOBSEC think tank. Fewer than 10 percent of Hungarians said they would even consider leaving the military alliance.
Mr. Kreko said that Mr. Orban, in traveling to Moscow at the height of tensions with the West, was handing Mr. Putin a foreign policy victory by showing that the European Union and NATO are divided over Ukraine.
Tuesday’s news conference with Mr. Putin constitutes a “loyalty test” for Mr. Orban, Mr. Kreko said.
“If he doesn’t contradict Putin when talking about the Ukraine crisis, then we have an issue,” he said.