The local governor and the Ukrainian military say troops restored a border marker and sent a message to President Zelenskyy: "Mr. President, we have reached it. We are at the border."
As the new week begins, the battle for eastern Ukraine continues to be both bloody and uncertain, with Russian forces focusing their attacks on the Donetsk region in the east.
Meanwhile, Sweden and Finland's moves to join NATO have raised tensions with Russia, and negotiations over a new set of EU sanctions continue to hit roadblocks.
See our blog below for a summary of Monday's key developments or watch our live coverage in the player above.