It took barely a week of street protests by environmentalists in January 2012 before Boyko Borisov, Bulgaria's prime minister, relented and cancelled a licence for Chevron, the US energy company, to explore for shale gas in the Balkan country's prime wheat-growing region.
When another wave of protests prompted by sharp rises in electricity and fuel prices toppled Mr Borisov's centre-right government 13 months later, it seemed as if civil society had finally come of age in the EU's poorest member state.
Yet some in Sofia believe a Russian hand helped foment the protests for its own ends. They point to Kremlin links to local groups that supplied demonstrators and funded an anti-shale media campaign. The goal, they believe, was to punish the pro-European Mr Borisov for pursuing policies that might reduce Bulgaria's dependence on Russian energy.
"We must remember the anti-shale protests and the other organised actions against the government of Boyko Borisov. This was a well-planned scenario developed by local corporate, oligarch and economic interests connected with Russia," said Tsvetan Tsvetanov, a former interior minister who is a close Borisov confidant.
Other Bulgarian officials also allege Russian involvement, but declined to be identified or supply hard evidence to substantiate claims that Moscow was funding Bulgarian political parties, among other forms of meddling. Several parties under suspicion have denied any involvement.
Still, the episode embodies a broader worry now gripping European capitals: that Russia is increasingly using an array of tools - from propaganda to energy supplies and cash - to reassert its dominance in eastern Europe and the Balkans. Anders Fogh Rasmussen, then Nato secretary-general, said some alliance members had reported "sophisticated information and disinformation operations" by Russia against shale gas.
Angela Merkel, the German chancellor, voiced her fears during the recent G20 summit in Australia, warning that the Kremlin's ambitions extended beyond Ukraine to vulnerable states in southeast Europe. US and Bulgarian diplomats also fret about the depth of Russian influence still pervading a country that was once the Soviet Union's closest ally.
"Moscow's approach is clear: they want to ensure that Bulgaria is an unreliable partner for the EU and Nato," said Ilian Vassilev, managing partner of Innovative Energy Solutions, a Sofia-based consultancy, and former Bulgarian ambassador to Moscow. "The destabilisation effort used to happen under the radar but it's in the open now because of worsening problems over Russian-backed energy projects as a result of the conflict in Ukraine."
The tabular content relating to this article is not available to view. Apologies in advance for the inconvenience caused. > Even though Bulgaria joined the EU in 2007, it remains an inviting target for Russian soft power. An older generation still harbours nostalgia for the communist past. Bulgarians also have a tradition of respect for the Russian military's role in liberating part of the country in 1877 from Ottoman Turkish rule.
These days, energy has been at the centre of the relationship. Russia's Gazprom supplies 90 per cent of Bulgaria's annual gas via a pipeline that runs through Ukraine. Its dominance means that Bulgaria's state energy company - despite its relative poverty - pays 30 per cent more for its gas than importers in Germany.
For Mr Borisov, a one-time bodyguard, the drive to exploit the country's shale gas deposits through the Chevron deal was one hope of addressing this. If successful, the Chevron venture might have allowed the country to diversify its energy supplies and drive a better bargain with Gazprom.
It was not Mr Borisov's only affront to Moscow. In January 2013, he called off a €7bn project backed by previous governments to build a 2,000-megawatt nuclear plant at Belene on the Danube river which was led by Russia's state-owned Rosatom group. His government also awarded a concession to explore for gas off Bulgaria's Black Sea coast to an international consortium headed by Total of France.
Those who suspect Moscow's involvement in the unrest in Sofia point to a media campaign - said to be worth €20m - backing the anti-shale protests. It was handled by several local media and advertising companies with Russian connections.
One person involved in the campaign described it as "unprecedented for Bulgaria", involving multiple environmental groups, paid protesters bussed in from around the country and a television blitz. The Socialist party, successors to the Communists who ruled Bulgaria in fealty to the Kremlin for four decades, took up the cause.
"The socialists came out against shale gas exploration in a big way," said a high-ranking former official. "Their party machine was active in organising the protests."
Sergei Stanishev, the former prime minister, rejected suggestions that the protests were anything but legitimate, and were spurred by the Borisov government's rush to embrace shale drilling without first guaranteeing health and safety standards.
"Many of our youth or regional activists have participated in protests with their names and faces. However, my party has never been a leading or directing force in this broad civil movement," he said in an email to the Financial Times.
A far-right Bulgarian political party, Ataka, was a prominent backer of the electricity protests. Its leader, Volen Siderov, is so enthusiastically pro-Russian that he chose to launch his party's campaign for this year's European parliament elections not in Sofia but Moscow.
At least two former Bulgarian government advisers believe the party received funding through the Sofia branch of Russkiy Mir, an Orthodox cultural foundation founded by Russia's president Vladimir Putin as a vehicle for exercising soft power abroad - although Miglena Alexandrova, an Ataka MP, denies this.
"It is definitely not true that the party has received any funding from the Russian foundation. Ataka is entirely financed from its state subsidy," she said.
Still, some former Bulgarian officials remain convinced of the Kremlin's role. "They have the capacity to mobilise, they make cash payments and arrange transport for protesters," one said. "At the same time, they're adept at using social media to attract genuine participants like the environmental groups."
Mr Borisov, who declined to comment, may now be bracing for further confrontation with Moscow. His centre-right Citizens for the European Development of Bulgaria party, known as Gerb, finished first in last month's general election, returning him to the prime minister's office.
One of the first issues confronting him will be Bulgaria's participation in the Gazprom-backed South Stream pipeline, intended to carry Russian gas across the Black Sea to central Europe, bypassing Ukraine.
The outgoing socialist-led government was a keen backer of South Stream. Even though it suspended participation in June under pressure from Brussels it still allowed on-the-ground preparations to continue.
The costs of the project have spiralled: estimates for the 450km Bulgarian stretch have soared from €1.2bn in 2010 to €3.8bn today. Still, it is popular among many Bulgarians who recall supply cuts to city heating plants and industry in January 2009 when Russia shut off gas flows to Ukraine in subfreezing temperatures.
"South Stream would mean security of supply for Bulgaria," said Delyan Dobrev, a former energy minister. "But the disadvantage is that it doesn't reduce our dependence on Gazprom."
Additional reporting by Dessislava Borislava
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