Trump had already clashed with Khan in the wake of a driver plowing into pedestrians on Westminster Bridge in March, the first of two terror attacks to hit London in the last three months. The second incident, which occurred last weekend on London Bridge, prompted Trump to mock Khan via his Twitter account: “At least 7 dead and 48 wounded in terror attack and Mayor of London says there is ‘no reason to be alarmed!'”

At least 7 dead and 48 wounded in terror attack and Mayor of London says there is "no reason to be alarmed!"

— Donald J. Trump (@realDonaldTrump) June 4, 2017

Khan had used the phrase in the context of the extra police presence to be expected on the streets in the wake of the attack, rather than downplaying the seriousness of the terrorist threat. (His exact words were: “Londoners will see increased police presence today and over the course of the next few days. There’s no reason to be alarmed.” You can read the full statement from which the quote was lifted here.)

Observers quickly noted that Trump took Khan’s words out of context. In response to the criticism, Trump doubled down on his position Monday, tweeting: “Pathetic excuse by London Mayor Sadiq Khan who had to think fast on his “no reason to be alarmed” statement. MSM is working hard to sell it!”

Pathetic excuse by London Mayor Sadiq Khan who had to think fast on his "no reason to be alarmed" statement. MSM is working hard to sell it!

— Donald J. Trump (@realDonaldTrump) June 5, 2017

“MSM” is an acronym for “mainstream news media.”

It’s unclear if Trump had consulted with the U.S. embassy in London before publishing his newest tweets. There, acting ambassador Lewis Lukens had earlier praised Khan for his “strong leadership” in the wake of a “heinous attack.” London is one of a number of U.S. embassies around the world without an ambassador due to delays in appointments that President Trump blames on “obstructionist” Democrat lawmakers.

I commend the strong leadership of the @MayorofLondon as he leads the city forward after this heinous attack. – LLukens 3/3 https://t.co/p4dDZuCpyO

— U.S. Embassy London (@USAinUK) June 4, 2017

The response from emergency services, law enforcement & officials in Ldn–as well as ordinary Londoners–has been extraordinary. – LLukens 2/3

— U.S. Embassy London (@USAinUK) June 4, 2017

In similar vein, Prime Minister Theresa May refused to endorse Trump’s criticism Monday, saying after a speech that Khan, who is a member of her political opposition, the Labour Party, was doing “an excellent job.” A YouGov poll said a clear majority of Londoners still trusted to keep the city safe from terrorists by a margin of 51 to 30.

Khan himself hasn’t responded to Trump’s tweets. A spokesperson for Khan was quoted as saying that the mayor has “more important things to do than respond to Donald Trump’s ill-informed tweet that deliberately takes out of context his remarks.”

Earlier Monday, London City Hall said it had installed security barriers overnight on three prominent London bridges—Waterloo, Lambeth and Westminster—with the aim of stopping any cars from mounting the sidewalk and driving intentionally into pedestrians.

New barriers on Westminster bridge apparently a security measure following the terror attacks. pic.twitter.com/qdTpvQZtmL

— Ellie Price (@EllieJPrice) June 5, 2017

The tactic had been used in both of this year’s attacks in London. In March, an attacker mowed down crowds of tourists outside the Houses of Parliament before stabbing a police officer to death under Big Ben itself. On Saturday, three attackers in a van did the same to pedestrians on London Bridge and continued their killing spree on foot before being shot by armed police.

ISIS has claimed responsibility for the attack. According to The Times newspaper of Britain, police have so far arrested 12 people in connection with the attack, and have released one without charge.