The European Union's foreign policy chief Federica Mogherini on Monday deplored the poisoning in the UK of a former Russian spy and his daughter earlier this month, calling it "absolutely unacceptable".
"It is absolutely clear that the United Kingdom has our full solidarity and we are extremely concerned at what happened," Mogherini told reporters in Brussels.
"It is absolutely unacceptable," she said on the sidelines of an EU foreign ministers' meeting.
Mogherini's comments came after Vladimir Putin was re-elected Russian president for a new six-year term with over 76 percent of the vote according to official figures - to a muted Western reaction.
Britain has claimed that Putin "in all probability" personally ordered the poisoning of Sergei Skripal and his daughter Yulia with a military-grade nerve agent in the southern English town of Salisbury two weeks ago.
Putin on Sunday dismissed the allegation as "rubbish" and said Russia no longer possessed such chemical weapons.
The Skripals are fighting for their lives in hospital in the UK and their attempted murder has sparked a diplomatic rift between the British and Russian governments.