VILNIUS, Lithuania — Decades after leaving the Soviet Union, the Baltic countries of Estonia, Latvia and Lithuania this weekend will flip a switch to end electricity-grid connections to neighboring Russia and Belarus — and turn to their European Union allies.

The severing of electricity ties to oi- and gas-rich Russia is steeped in geopolitical and symbolic significance. Work toward it sped up after Russian President Vladimir Putin ordered his troops to invade Ukraine three years ago, battering Moscow’s EU relations.

“This is physical disconnection from the last remaining element of our reliance on the Russian and Belarusian energy system,” Lithuanian President Gitanas Nauseda told The Associated Press recently.

EU chief Ursula von der Leyen and other dignitaries are expected at a ceremony on Sunday as a specially made 29.5-foot-tall clock in downtown Vilnius counts down the final seconds of the Baltic states’ electricity ties to Russia.

The Baltic countries, which are all NATO members, have often had chilly ties with Russia since declaring independence from the USSR in 1990, and relations soured further over Russia’s full-scale invasion of Ukraine in 2022.

Sixteen power lines that used to connect the three Baltic states with Russia and Belarus were dismantled over the years as a new grid linking them with the rest of the EU was created, including underwater cables in the Baltic Sea.

On Saturday, all remaining transmission lines between them and Russia, Belarus and Russia’s Kaliningrad — a Russian exclave wedged between EU members Poland and Lithuania and the sea — will be switched off one by one.

Then, for 24 hours, the Baltic Power System will operate solo in an “island operation mode.” The next day, the power system is set to merge with the Continental European and Nordic grids through several links with Finland, Sweden and Poland.

The Kaliningrad region, which has no land ties to mainland Russia, already relies on its own power generation, according to Litgrid, Lithuania’s electricity transmission system operator.

Kremlin spokesman Dmitry Peskov said that the disconnection plan was announced in advance by the Baltic countries and the Russian energy sector had taken preparatory steps to ensure smooth operation on its side.

“Those plans were announced long time ago, and they required certain actions by our and their electric companies,” Peskov told reporters. “We have taken all necessary measures to ensure reliable and uninterrupted operation of our unified energy system.”

The three Baltic countries, which together share a 1,015-mile-long border with Russia and Belarus, officially informed Moscow and Minsk of the disconnection plan in July. Their national transmission system operators credited 1.2 billion euros ($1.25 billion) in EU and other support to help the countries synchronize with the Continental Europe Synchronous Area.

“Lithuania has done a lot in the last 30 years to disconnect, to become independent,” Nausėda said. Three years ago, “we stopped buying any kind of energy resources from Russia. It was our response to the war in Ukraine.”

Despite the advance notice, the Baltic nations are still on watch for a possible response from their former Soviet partners.

“The risk of cyberattacks remains substantial,” Litgrid said last week, adding that continued vigilance, collaboration, defensive steps and “robust” cybersecurity measures were needed to effectively mitigate potential threats.

Latvian Prime Minister Evika Siliņa warned Wednesday of possible provocations, but said Latvia was well-prepared and services including the armed forces and national guard were stepping up their vigilance and security measures.

“Clearly there are risks, we understand that very well. But the risks are identified and there is a contingency plan in case these risks materialize,” Siliņa said.

After the disconnection plans were announced, propaganda campaigns cropped up on social media and in printed leaflets in city streets that issued fake-news warnings about blackouts, severe energy shortages and sky-high energy bills for consumers.