European Union leaders will discuss new, tough sanctions on Russia at an emergency meeting later on Thursday in reaction to its attack on Ukraine, the 27-nation bloc's officials said.

"With this package, we will target strategic sectors of the Russian economy by blocking their access to key technologies and markets," European Commission chief, Ursula von der Leyen said in an emergency statement.

"In addition, we will freeze Russian assets in the EU and stop the access of Russian banks to the European financial market."

The EU approved a first round of sanctions on Wednesday, including blacklisting Russian politicians and curbing trade between the EU and two breakaway regions of eastern Ukraine whose independence Putin has recognized.

The first round of sanctions include a sectoral prohibition to finance the Russian Federation, its government and central bank.

Within the existing framework for sanctions, EU will extend restrictive measures to cover all the 351 members of the Russian State Duma and impose targeted restrictive measures on additional 27 high profile individuals and entities, according to the Wednesday announcement.

Restrictive measures include an asset freeze and a prohibition from making funds available to these listed individuals and entities.

The new measures to be discussed at an evening summit of national EU leaders starting at 1900 GMT will be "the harshest package of sanctions we have ever implemented," the bloc's foreign policy chief Josep Borrell said.

(With input from Reuters)