Fishing in Serbia’s troubled waters after a contested general election, Russia on Monday accused the West of orchestrating anti-government street protests in Belgrade, the Serbian capital, that flared into violence on Sunday evening.

Claims of a Western plot by Russia’s ambassador to Serbia, Alexander Botsan-Harchenko, were the latest efforts by Moscow to thwart a so far mostly fruitless diplomatic campaign by the United States and Europe to lure Serbia out of Russia’s orbit and break traditionally strong ties between the two Slavic and Orthodox Christian nations.

Previously peaceful street protests in Belgrade over what the opposition says was a rigged general election on Dec. 17 turned ugly on Sunday after protesters tried to storm the capital’s City Council building and were met by volleys of tear gas from riot police officers.

The Russian ambassador, in a television interview, said there was “irrefutable evidence” that the “riot” had been incited by the West. This echoed claims by Serbia’s strongman leader, President Aleksandar Vucic, that his government had come under attack from outside forces seeking a “color revolution,” a term coined by Russia to describe popular revolts that it invariably dismisses as Western conspiracies.

“This was an attempted violent takeover of the state institutions of the Republic of Serbia,” Mr. Vucic told Pink TV, a pro-government television station, deriding accusations of election irregularities as “lies” ginned up by his political opponents.

There is no evidence that Western governments instigated the past week’s street protests against Mr. Vucic and what his opponents believe was a stolen Belgrade election.

Protests against the election continued on Monday. A demonstration led by university students attracted only a modest turnout but blocked traffic on a central Belgrade street to government headquarters.

A report last Monday by election monitors from the Organization for Security and Cooperation in Europe said that Serbian voters had been given a wide choice of candidates and that “freedom of expression and assembly were generally respected.” But, it said, the governing party had enjoyed a “tilted playing field” because “pressure on voters as well as the decisive involvement of the president and the ruling party’s systemic advantages undermined the election process overall.”

Mr. Vucic’s governing Serbian Progressive Party trounced the opposition in this month’s parliamentary vote but fared less well in an election for the Belgrade City Council, eking out a narrow win that the opposition attributed to voters whom they say were illegally bused into the capital from other areas of the country and from neighboring Kosovo and Bosnia.

While accepting defeat in the vote for a new Parliament, the opposition vowed to overturn what it sees as a rigged result in the Belgrade municipal election and has staged daily street protests over the past week.

Western countries, wary of burning bridges with Mr. Vucic, have been muted in their criticism of the election. The U.S. ambassador to Serbia, Christopher R. Hill, last week called on the country to address “deficiencies” in the electoral system but stressed that “the U.S. government looks forward to continuing our work with the Serbian government” and bringing it “more fully into the family of Western nations.”

Serbia applied to join the European Union in 2009, but its application has been stalled for years. There has been growing pressure from the West on Mr. Vucic to pick a side since the start of Russia’s full-scale invasion of Ukraine in February last year.

Mr. Vucic condemned Russia’s invasion of Ukraine but has balked at joining European sanctions on Russia and shown only fitful interest in settling a long-running dispute over the status of Kosovo, formerly Serbian territory that declared itself an independent state in 2008. Kosovo, inhabited largely by ethnic Albanians, severed its ties to Serbia after a 1999 NATO bombing campaign against Belgrade and other cities that left even many pro-European Serbs deeply suspicious of the West’s intentions.

Bad blood has slowly eased between Serbia and the West, which blamed Kosovo, not Mr. Vucic, for exacerbating tensions after a flare-up of violence in mainly Serb areas of northern Kosovo in September. That stance led to accusations of “appeasement” of Belgrade from European politicians and commentators who see Mr. Vucic as the principal threat to peace in the Balkans.

Instead of giving Mr. Vucic more leeway to break with hard-line Serbian nationalist forces closely aligned with Russia as Washington had hoped, the recent election appears to have only pushed him closer to Moscow.

After the clashes in Belgrade on Sunday evening, Serbia’s prime minister Ana Brnabic, a close ally of Mr. Vucic, thanked Russian security forces for sharing information pointing to a Western hand in the opposition protests.

“It probably won’t be popular with those from the West, but I feel especially tonight that it is important to stand up for Serbia and to thank the Russian security services that had that information and shared it with us,” Ms. Brnabic said.