MOSCOW — On a rainy afternoon this week, a group of Russian officials and oil executives gathered for Mass in a Catholic church tucked away behind the imposing secret service headquarters in central Moscow.

They did not come to pray. Instead, they were commemorating the late Venezuelan leader Hugo Chávez, who poured billions of dollars into Russian weapons and machinery, and showing support for his embattled successor, Nicolás Maduro.

Mr. Maduro is fighting to save the political system he and Mr. Chávez have built, with Russian support, for two decades. Mr. Maduro’s catastrophic economic mismanagement has led the opposition to claim the country’s leadership with the support of the United States, the European Union and most South American nations.

To Russia, it was the latest attempt by the West to topple an adversarial government and check President Vladimir V. Putin’s global outreach. The Kremlin reacted by closing ranks around Mr. Maduro and offering him unequivocal diplomatic support, which was on display at St. Louis of France Church on Wednesday.