Belarus is suspending its participation in the Eastern Partnership, an initiative to boost ties between the EU and its ex-Soviet neighbours.
The move comes as Brussels imposed new sanctions over the forced landing of a European flight last month.
The European Union, United States, Britain and Canada sanctioned Belarus after a Ryanair passenger flight between European capitals was grounded in Minsk, where authorities detained opposition activist Roman Protasevich and his girlfriend who were on board.
They were the latest in a series of penalties against President Alexander Lukashenko, who has ruled Belarus for nearly three decades.
Mr Lukashenko clamped down on the opposition after mass protests erupted following disputed presidential elections last year.
Belarus "cannot fulfil its obligations under this agreement in the context of sanctions and restrictions imposed by the EU," the Belarusian foreign ministry said in a statement today.
It said that Belarus's representative to the EU had been recalled to Minsk for consultations and "invited" the head of the EU Delegation to Belarus to return to Brussels and "convey to his leadership the position of the Belarusian side".
The ministry also said the suspension of the agreement will have a "negative impact" on fighting illegal migration and organised crime, as Belarus shares a border with EU members Poland and Lithuania.
Earlier in June, Lithuanian border guards reported a sharp increase in migrants arriving from across the Belarus border, saying it suspected that Belarusian authorities allowed them to pass.
EU chief Charles Michel said Belarus's decision to leave the Eastern Partnership was "another step backwards" that would "escalate tensions further".
Belarus has taken another step backwards today by suspending its participation in the Eastern Partnership.
— Charles Michel (@eucopresident) June 28, 2021
This will escalate tensions further and have a clear negative impact on the people of Belarus by depriving them of opportunities provided by our cooperation.
The EU launched its Eastern Partnership initiative in 2009, offering six former-Soviet states improved economic and political ties in return for reforms. Those countries were Belarus, Ukraine, Moldova, Armenia, Azerbaijan and Georgia.
Brussels insists the partnership, seen by some countries as a precursor for joining the EU, is "not aimed at any country" but Moscow has long seen it as an attempt to encroach on territory long in Russia's sphere of influence.
Mr Lukashenko, 66, was invited to the summit for the first time in 2017, after sanctions against him and other officials were lifted in a move to encourage progress on human rights in Belarus.
Opposition politician Svetlana Tikhanovskaya said that the move to leave the Eastern Partnership "only shows weakness and shortsightedness" of the current regime.
