Prime minister said that there was a ‘strong connection of a foreign factor’ in alleged conspiracy to take over the Montenegrin parliament on election day

Montenegro’s long-serving prime minister is to step down, the governing Democratic Socialist party has said, and will be replaced by his deputy, Duško Marković.

Tuesday’s announcement came hours after Milo Đukanović, who has governed as Montenegro’s prime minister or president for a total of 21 years since 1991, announced his government was investigating a possible Russian role in an alleged 16 October coup plot aimed at derailing the country’s elections.

It is unclear whether there is any connection between Đukanović’s claims of a coup and his abrupt departure. Party officials were quoted as saying that he would be replaced by Marković as its candidate for prime minister if it was able to secure a majority coalition in post-election negotiations.

Đukanović, whose time in office has been dogged by allegations of authoritarianism and corruption, has retired from leadership on two previous occasions, in 2006 and 2010, before returning to the helm.

Đukanović had said there was a “strong connection of a foreign factor” in the alleged conspiracy to take over the Montenegrin parliament on election day, adding that the country’s authorities would investigate the extent of involvement of Russia and Serbia. Twenty people, including the former commander of special police in neighbouring Serbia, were arrested on the day of the would-be coup attempt.

The Serbian prime minister, Aleksandar Vučić, announced on Monday night that Serbian police had made more arrests of people suspected of following Đukanović and planning unspecified crimes in Montenegro.

“We have seized uniforms, money and other things, and have informed the special prosecution in Montenegro of what we know,” Vučić told a press conference. He said the suspects had no connection to the Serbian state but did have ties to an unnamed third country.

Russia’s security chief, Nikolai Patrushev, was expected in Belgrade to hold talks with Serbian leaders in the wake of the arrests, according to reports from the Serbian capital. Those reports said Patrushev had come to discuss terrorism, the migrant crisis in Europe and alleged extremism in Kosovo.

Đukanović faced stiff opposition from a pro-Russian coalition opposing the country’s proposed membership of Nato. Leaders of the Democratic Front made frequent visits to Moscow in the run-up to the election. Đukanović’s party won the vote, but not an absolute majority, and Montenegro’s Nato membership is awaiting ratification by member states.

Bratislav Dikić, the former commander of the Serbian gendarmerie who was arrested on 16 October in Montenegro, has denied involvement in any coup attempt, saying Montenegrin police had planted a phone on him as well as keys to a warehouse containing weapons.

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The Montenegrin prosecutor’s office said last week it had reasonable suspicion that a criminal group had been formed in Serbia and Montenegro with the intention of attacking the police guard at the parliament in Podgorica, taking over the assembly and declaring the winner of the election.

Seventeen years after the Kosovo war, the last of the conflicts that marked the disintegration of Yugoslavia, tensions are still high in the region. Serbia, backed by Russia, refuses to recognise Kosovo’s independence, while Bosnia’s sovereignty is under constant pressure from Serb and Croat separatists. Stjepan Mesić, a former Croatian president, claimed that leaders of both communities were seeking to break up Bosnia, warning that it could lead to a new war.

Adding to the febrile atmosphere, the Serbian government announced that an interior ministry official had been arrested for contacts with western intelligence. The interior minister, Nebojša Stefanović, said the authorities had “neutralised this person through effective action” but gave no further details.