WASHINGTON (AFP) - The United States is planning a new set of "severe" sanctions on Russia over the alleged attempt by Kremlin agents to kill a turncoat spy in Britain, a State Department official said on Thursday (Sept 13).

Assistant Secretary of State Manisha Singh told a congressional hearing that Russia has not yet accepted demands that it come clean about its production of the Novichok nerve agent used in the March 4 attempt to kill former double agent Sergei Skripal and his daughter in Salisbury, England.

Moscow was given until November to allow on-site inspections of facilities linked to the potent poison and to provide "verifiable" assurances that Novichok will not be used again.

"They have not done so so far," Ms Singh said.

"We are looking at this November deadline absolutely, we plan to impose a very severe second round of sanctions," she said.

She said the new sanctions will include banking sanctions, a broader ban on Russian procurement of defence articles, and a block on any foreign aid.

The first sanctions over the Skripal poisoning were implemented in August, halting foreign aid to Russia except for humanitarian assistance and for food and other agricultural products; blocking some defence sales; and banning government credit support for exports to Russia.

Moscow has denied the allegations.

But last week Britain identified two Russians it said carried out the assassination attempt and said they were officers of the GRU Russian military intelligence service.

London pointed a finger at Russian President Vladimir Putin as "ultimately responsible" for the crime.

Leaders of Canada, the United States, France and Germany expressed "full confidence" in the British assessment.

On Thursday, the two suspects appeared on Russian television to deny they worked for the GRU and said they were in Salisbury as tourists.

"They are civilians," Mr Putin said late on Wednesday, adding there was nothing criminal about them.