Upon arriving in Brussels for the EU summit focused on the bloc's partnership with eastern European countries, the Prime Minister offered a stark assessment of Russian President Vladimir Putin's actions.
Speaking ahead of the Eastern Partnership summit, Mrs May said: "The summit here today is all about taking stock and about looking ahead to see how we can tackle the shared challenges together, both in security and development.
"We must be open-eyed about the actions of hostile states like Russia who threaten the potential growth of the Eastern Neighbourhood and who try to tear our collective strength apart.
The Prime Minister will use the EU summit, which will also be attended by the leaders of Ukraine, Georgia, Moldova, Armenia, Azerbaijan and Belarus, to reaffirm Britain's support to eastern Europe.
She will highlight the UK's £50m spend to support reform and security in the region via projects such as tax reform in Moldova and de-mining in Ukraine; as well as pointing to Britain's pledge of £100m over five years to counter disinformation in the EU's neighbouring countries.
As it was reported earlier British Prime Minister Theresa May accused Russia of meddling in elections and spreading fake stories in the media in an extraordinary attack on its attempts to “weaponise information” in order to sow discord in the west.
The prime minister spoke out against “the scale and nature” of Russia’s actions during an address at the lord mayor’s banquet, saying it was “threatening the international order on which we all depend”.