Moscow has warned of retaliation after the US announced plans to impose new sanctions against Russia over the Salisbury nerve agent attack.

The US made the announcement yesterday, accusing the Russian government of being behind the 'attempted assassination' of former spy Sergei Skripal and his daughter Yulia.

Chemical weapons experts have said that the nerve agent novichok - which was developed in the Soviet Union - was used in the attack.

US officials have also warned that Russia could face a second round of 'more draconian' sanctions if it does not meet a series of 'pretty demanding' conditions in 90 days.

The first round of sanctions is due to go into effect around August 22nd, following a notice period given to US Congress.

The Kremlin has repeatedly denied any responsibility for the Salisbury attack, and today slammed the new sanctions.

Russian foreign ministry spokesperson Maria Zakharova said the conditions for lifting the sanctions are 'unacceptable'.

In comments quoted by the TASS news agency, she argued: "The US is intentionally choosing the path of a further deterioration of bilateral relations, which have been nearly reduced to zero thanks to its efforts."

She said the Kremlin is considering a tit-for-tat response in retaliation, noting: "The Russian side will engage in working out retaliation measures to a new unfriendly move by Washington."

A Kremlin spokesperson, meanwhile, said the sanctions "don't conform to international law", while a Russian representative to the UN described the situation as a "theatre of the absurd".

The theater of absurd continues. No proofs, no clues, no logic, no presumption of innocense, just highly-liklies. Only one rule: blame everything on Russia, no matter how absurd and fake it is. Let us welcome the United Sanctions of America! #SkripalHoax https://t.co/MekROW5WBc

— Dmitry Polyanskiy (@Dpol_un) August 8, 2018