Russian forces pressed on with their offensive across several Ukrainian regions on Monday, while President Volodymyr Zelensky warned of the potential for more serious attacks ahead of Ukraine’s 31st anniversary of independence from Soviet rule.

Artillery shells rained down on Nikopol, near Zaporizhzhia - Europe’s biggest nuclear plant, while missiles struck near the Black Sea port of Odesa over the weekend. Zelensky has called for vigilance, saying Moscow could try “something particularly ugly” ahead of Wednesday, which marks Ukraine’s Independence Day and also half a year since Russia invaded Ukraine on Feb. 24. Zelensky said he had discussed “all the threats” with French President Emmanuel Macron and word had also been sent to other leaders including Turkish President Tayyip Erdogan and U.N. Secretary-General Antonio Guterres.