Fighting got underway Sunday in Kharkiv, Ukraine’s second-largest city, after Russian forces stormed in from the outskirts, according to reports.

The airspace over Ukraine is still being contested as Ukrainian forces continue to fight back against the Russian invasion, according to a senior U.S. defense official on Sunday.

The European Union on Sunday announced plans to close its airspace to Russian planes, and fund weapons for Ukraine to defend against Russia's invasion of its western neighbor, according to international officials.