Moscow on Friday ordered the US to slash its number of diplomats in Russia and froze two embassy compounds in a pre-emptive strike against tough new sanctions being readied in Washington.

On Thursday, the US Senate passed new bipartisan sanctions on Russia, Iran and North Korea, sending the package to President Donald Trump.

White House spokeswoman Sarah Huckabee Sanders said Trump will sign the bill into law, ending speculation over whether he would veto the measure.

But the president only did so after negotiating "critical elements" of the bill, the spokeswoman added, without specifying what those elements were.

"He has now reviewed the final version and, based on its responsiveness to his negotiations, approves the bill and intends to sign it."

The move was a further blow to hopes in Moscow that Trump's election might help improve ties that slumped to their lowest point since the Cold War over the Kremlin's meddling in Ukraine and alleged interference in the US election.

It has also upset some European nations fearful that it could hit their businesses. Germany warned it would not accept sanctions that targeted companies involved with Russia's energy sector.

The Kremlin had previously said it would hold off from responding until the sanctions became law. But it appeared to change tack after President Vladimir Putin insisted Thursday that he could not "endlessly tolerate this kind of insolence."

A Russian foreign ministry statement demanded the US cut its diplomatic presence in Russia by September to 455 -- the same number Moscow has in the US -- in a move sources said could force out hundreds of diplomats.

It also said it was barring the US embassy from using a Moscow summer house and storage facility in the city from August 1.

"The United States under the absolutely invented pretext of Russian interference in their internal affairs takes one grossly anti-Russian action after another," it said.

Moscow "reserves the right to carry out other measures that could affect the interests of the US," the statement added.

- Revenge for Obama -

In a phone call later with US Secretary of State Rex Tillerson, Russian Foreign Minister Sergei Lavrov insisted that the measures from Moscow were a "necessary step," his ministry said.

Lavrov said that Russia was "still ready to normalise bilateral relations with the US and to cooperate on the most important international issues.

"However, this is possible only on the basis of equality, mutual respect and a balancing of interests," the ministry statement added.

Earlier, US Ambassador John Tefft "expressed his strong disappointment and protest" at the development, a spokesperson at the embassy in Moscow told AFP.

The spokesperson declined to comment on the current number of US diplomats and staff in Russia, but Russian wires cited "informed sources" saying hundreds of people would have to leave.

The punishment announced by Moscow closely resembled punitive measures announced by then President Barack Obama in December. That was over an alleged Kremlin hacking and influence campaign to sway the 2016 US elections in favour of Trump.

Obama ordered out 35 Russian diplomats and closed down two embassy summer houses that Washington said were being used by Moscow to spy on the US.

At the time, Putin made the surprise choice not to respond to the US move, saying that he was waiting to see how Trump handled the situation once he came to power.

Trump repeatedly insisted during his election campaign that he wanted to improve ties with Russia, sparking hope in the Kremlin for an improvement.

Moscow is already the subject of tough US sanctions over its annexation of Crimea from Ukraine and support for a bloody insurgency in the country.

But allegations from the US intelligence community that Putin interfered in the US elections to get Trump elected have made any concessions to Trump politically toxic.

The White House had opposed the new sanctions package that curbs Trump's ability to lift the punishment, but the near-total support in the US Senate and House put him in a major bind.

Even if Trump had decided to veto the bill, Congress could likely have mustered enough votes to override him.

Despite tensions over alleged Russian interference into the US election, Moscow and Washington have worked closer together on Syria.

The two countries thrashed out a ceasefire in the south of the war-torn nation despite being on opposing sides of the conflict.

Source: AFP