Boris Johnson has faced questions in parliament over the export of British arms and riot gear to US security forces after opposition parties called for shipments to be halted.
The prime minister said he would look into any concerns about the use of British-made weapons but insisted that a "scrupulous" system of checks was in place to ensure they were not misused.
Labour, the SNP, Liberal Democrats and Greens this week urged export licences for the equipment to be suspended pending an investigation into whether Britain might be aiding a crackdown that has seen police attack peaceful protesters and journalists.
During a session of prime minister's question time on Wednesday the Scottish National Party's leader in Westminster Ian Blackford accused the prime minister of having "skirted" the issue.
"Watching events unfold across America in recent days and the actions and rhetoric from the American president have been distressing and deeply worrying. We cannot delude ourselves to believe we are witnessing anything short of a dangerous slide into autocracy," Mr Blackford told the House of Commons.
"It is in times like these when people look to those they elect for hope, for guidance, for leadership and for action. However, in the seven days since George Floyd was murdered the UK government has not even offered words, has not expressed that pain. It has shuttered itself in the hope that no-one would notice."
Asked what representations he had made to "his ally Donald Trump" and whether black lives mattered, Mr Johnson replied: "Of course black lives matter, and I totally understand the anger, the grief that is felt not just around America but around the world and in our country, and I totally understand and I get that.
"I also support, as I've said, the right to protest. The only point I would make to the House is that protests should be carried out lawfully and in this country protests should be carried out in accordance with our rules on social distancing." He gave no account of any representations to Mr Trump.
Turning to the subject of weapons and equipment sourced from the UK, Mr Blackford told the prime minister: "It is imperative that the UK is vocal on human rights, freedom to gather and protest, freedom of speech and upholding press freedom in other parts of the world.
"It would be nothing short of hypocrisy if we were to turn a blind eye to events unfolding in the US. However, actions speak louder than words and the prime minister can shake his head, but the UK export millions of pounds worth of riot control equipment to the US including tear gas and rubber bullets.
He asked: "The prime minister must have seen how these weapons are used on American streets. With the government's own guidance warning against equipment being used in such a way, will the prime minister urgently review such exports?"
Mr Johnson told MPs: "I'm happy to look into any complaints but as he knows all exports are conducted in accordance with the consolidated guidance and the UK is probably the must scrupulous country in that respect in the world."
On Tuesday Labour's shadow international trade secretary Emily Thornberry wrote to her government counterpart with the same message, declaring that it would be wrong to sell weapons "at a time when Donald Trump is gearing up to use the US military to crush the legitimate protests taking place across America over the murder of black civilians". Amnesty International has also backed suspending exports and an investigation.
Government export licence records show that the US is one of the world's largest buyers of UK arms, with almost £6 billion worth licensed for export since 2010.
The licences have included £18 million worth of ammunition, including so-called "rubber bullets", smoke and pyrotechnic charges, CS gas grenades, and tear gas.
The sale of tear gas and rubber bullets specifically was done via an "open licence" system meaning the value of exports is not made public - in total three separate licences were approved for this equipment.
Britain has also licensed £800 million of small arms to the US since 2010, a proportion of which campaigners say likely to have been for police force use. The exports have included assault rifles, sniper rifles and other guns. Licences have also covered around £2 million in security goos such as riot shields.
The government's own licensing criteria says that exports should not be granted if there is a "clear risk that items might be used for internal repression". The government has the power to urgently review licences where situations change.
Asked about the issue at a regular briefing of journalists, the prime minister's spokesperson told reporters: “The PM answered a question on this in the Commons. All of our exports are conducted in line with strict guidelines and we operate one of the most robust licensing regimes in the world. Exports to the US are in accordance with that regime.”
Donald Trump has pledged to deploy the US military to clear the protests and urged local governors to use force to reclaim the streets if necessary. The demonstrations erupted first in the city of Minneapolis after the killing of black man George Floyd by a police officer, but quickly spread nation-wide.
The police response has seen security forces ramming crowds with cars, deploying gas and baton rounds against peaceful demonstrators, and arresting and shooting at domestic and international journalists covering events. Some looting of businesses has taken place during the chaos.
Andrew Smith of Campaign Against Arms Trade said: "The brutal and racist police violence we have seen over recent days has been absolutely appalling, and so has the reckless and totally irresponsible escalation from the President and his colleagues.
"These arms sales should never have been allowed and the government must ensure that they do not happen again. This kind of equipment is always repressive, and it can be deadly. There must be an urgent investigation into what weapons have gone over and if any of them have been used against protesters.
"Silence in the face of such injustice is compliance. We are always being told about the great relationship and influence that Boris Johnson has with the White House. If that is the case, then he must use it to condemn the violence in the strongest terms and call for widespread and structural change.
"Police violence and racism is not new, and nor is it exclusive to the US. Many of these issues will be familiar to people in the UK and beyond. It is time for police forces and politicians from across the world to consider their own roles and the systematic inequality that they are responsible for.”