Two further arrests have been made in relation to an alleged conspiracy to commit arson at a site connected to the Jewish community, the Metropolitan police have said.
The latest arrests, made by counter-terrorism police investigating the alleged arson conspiracy, were of a man aged 19 and another aged 26. They were detained in Watford on Tuesday and remain in custody.
Nine people have now been detained in relation to the same alleged arson conspiracy in the past four days.
The seven arrested before Tuesday have been released on bail, with strict conditions.
These include three men arrested in Harpenden on 19 April aged 24, 26 and 26. A 25-year-old man was also arrested in Stevenage.
A 26-year-old man and two women aged 50 and 59 were detained in a car near Birmingham on Monday in connection with the alleged conspiracy.
Separately, a teenager pleaded guilty on Tuesday to an arson attack on a synagogue in Kenton in north-west London on Saturday night.
The two new people arrested are suspected of being involved in planning an arson attack at an unknown venue related to the Jewish community.
The senior national coordinator of counter-terrorism policing, Vicki Evans, said: “Our investigations continue at pace, and we are continuing to identify and arrest suspects who we believe were involved in, or planning, the recent arson attacks in north-west London.
“We’ve now had the first conviction in relation to this recent spate of arson attacks and seven others have been charged. We remain determined to identify, arrest and charge all those who have been involved in the recent criminal activity.
“My message to anyone even considering getting involved in this type of activity is this: the stakes are high and it is absolutely not worth the risk.”
The arrests by counter-terrorism officers follow firebombings or attempted arson at synagogues and other Jewish targets across London.
These attacks started on 23 March, when ambulances run by a Jewish charity were set alight in Golders Green, north London. Then in April, there were attacks or attempted attacks on a charity, synagogues, and on an Iranian dissident media outlet.
Additional reporting by PA Media