The UK government on Thursday signed into law new legislation giving it powers to impose tougher and broader sanctions on Russia if Moscow steps up its aggression against Ukraine.

The new legislation entered force after being signed by a minister and formally laid before Parliament, a procedure that does not require a vote by MPs.

This came as UK Foreign Minister Liz Truss visited Moscow and met her Russian counterpart Sergei Lavrov, who said afterwards he was "disappointed" by the talks.

London said the new legislation was part of measures to "urge the Kremlin to end its campaign of aggression in Ukraine", as fears of an invasion grow.

The UK government said Minister for Europe James Cleverly had signed the legislation, providing a framework "for the strongest sanctions regime the UK has had against Russia".

British Prime Minister Boris Johnson told broadcasters in Warsaw that there must be "an automatic package of sanctions ready to go" if Russia attacks Ukraine.

He said this should include the Nord Stream 2 gas pipeline from Russia to Germany, calling this a "very, very important priority". 

The UK can now impose sanctions on Russian businesses and individuals in a "wide range of economic and strategically significant sectors", the government said, listing chemical, defence and IT industries and financial services.

The changes mean the UK can now impose sanctions not only on those who are "linked directly to the destabilisation of Ukraine", the Foreign Office said.

It can now target entities and businesses affiliated to the Russian government and their owners, directors and trustees.