France and Germany warned Russia on Monday of “serious consequences” if it tries to undermine Ukraine’s territorial integrity, amid concerns over a large military build-up at its border.

The foreign ministers of the two countries, Jean-Yves Le Drian and Heiko Maas, met with their Ukrainian counterpart Dmytro Kuleba in Brussels on the sidelines of a ministerial meeting of the Eastern Partnership, a forum that aims to improve the political and economic trade relations of the post-Soviet states of Armenia, Azerbaijan, Belarus, Georgia, Moldova and Ukraine.

Their meeting comes amid concerns that Moscow is preparing for a possible invasion of Ukraine’s border region. Ukraine’s President Volodymyr Zelensky has claimed that Russia has amassed nearly 100,000 troops at his country’s border.

Concerned with the buildup of troops and military equipment, Le Drian and Maas called on Russia “to adopt a posture of restraint and to be transparent about its military activities.”

- Any further attempt to undermine the territorial integrity of Ukraine would have serious consequences - said a joint statement from the two ministers.

This is the second time since April that Ukraine is faced with a security crisis at its borders with Russia.

To de-escalate the situation, France and Germany had proposed to Russia to join in talks with Ukraine under the existing ‘Normandy Format,’ which was used in 2014 to resolve the Donbas conflict. However, Moscow refused the offer.

Expressing concern over the deterioration of the security situation in eastern Ukraine’s Donbas region, the two ministers once again urged Russia to restart the joint dialogue and to fully implement the Minsk agreement.

After Russian forces invaded Donbas and annexed the Crimean Peninsula in 2014, France and Germany along with Ukraine led the initiative to enter into talks with Russia. Kyiv and Moscow and the Organization for Security and Co-operation in Europe (OSCE) signed the Minsk Protocol to implement a peace plan and end the fighting. But the agreement has failed to achieve success as Russia continues to support rebels in fighting Ukrainian government troops in Donbas.