British police scoured sections of Salisbury and Amesbury in southwest England, searching for a container feared to be contaminated with traces of the deadly nerve agent Novichok.
Dawn Sturgess, 44, later died in hospital.
How did the USA respond?
Our provision of foreign assistance is a tool of USA power and influence, and we're not going to foreswear that just because we have the obligation to impose some sanctions against Russian Federation. It kicked out 60 diplomats - the highest number of any country. It would also impose mandatory sanctions on individuals found to have taken part in the interference.
The government said Thursday it has begun working on ways to answer the measures.
Those slated for August are likely to include an export ban on sensitive national security technology and goods.
The sanctions enacted so far this year, and the threat of more, have already inflicted pain on Russia's middle class. Many exports and imports may also be cut off. Lev Gudkov, director of Russian independent pollster Levada Center, said it was quite possible that Putin would see a boost in his approval rating as a result of the sanctions, even though economic challenges could harm him in the long term.
Russian President Vladimir Putin has previously denied allegations that Russia was behind the poisonings, saying in March that it was "unthinkable that we would do such a thing".
Mr Trump was widely condemned over this.
According to commentators, the move by the U.S. is not just about following legislation.
"So linking these events is unacceptable to us, and just as with previous USA sanctions we believe are absolutely illegal and against worldwide law", Peskov told reporters. "And our American partners should realize this", the prime minister said.
He said Trump's tough actions are having an impact on Russian Federation, whose economy is already "in the toilet". His Twitter account is noticeably quiet; there is no mention of standing with America's allies in Europe against blatant terrorism.
The sanctions are expected to take effect later this month.
Angrily, to say the least.
The Kremlin said the new sanctions were "illegal and do not correspond to worldwide law".
"We have grown accustomed to not hearing any facts or evidence".
The White House said Trump provided "a letter of introduction" at Paul's request, and that the president "mentioned topics of interest that Senator Paul wanted to discuss with President Putin". What's more, we can not even say for sure what exactly and how it was used in Britain, since we don't have any information or any response to our proposal for a joint investigation with Britain into this incident, which concerns us greatly. "No answer has followed so far".
"Making a linking to these events (the British poisoning) is for us unacceptable and such restrictions like those passed by the American side earlier ... are absolutely illegal and do not correspond to global law", said Kremlin spokesman Dmitry Peskov, according to a Reuters report.
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