Russia warned foreign diplomats in Kyiv that it would attack the city if Ukraine disrupted World War II commemorations in Moscow this weekend, as attacks from both sides continued into Thursday.

Russia did not elaborate on its threat, and Ukraine did not immediately respond.

Russia and Ukraine traded strikes on Thursday, wounding 13 people in the Russian border city of Bryansk and one person in Ukraine’s Dnipro, officials from both sides said.

Russia marks World War II Victory Day each year on 9 May with a massive military parade through Red Square.

The country this week declared a unilateral ceasefire with Ukraine between 8 and 9 May to coincide with the commemorations.