British police investigating Friday's sword attack outside Buckingham Palace in London arrested a second man on Sunday, as the world-famous Notting Hill Carnival kicked off under increased security measures.
"The man was arrested on suspicion of being involved in the commission, preparation or instigation of terrorism at 10:15hrs (0915 GMT) today and he has been taken into custody," a police statement said.
It came hours after Islamic State jihadists claimed responsibility for Friday's knife attack on patrolling soldiers in Brussels, and as authorities in Spain revealed that the death toll from last week's twin attacks in Barcelona had risen to 16.
British police said they had arrested a 30-year-old man at an address in West London and were searching a property as part of the inquiry.
A warrant for the extended detention of the 26-year-old man involved in Friday's incident has also been granted, the statement said.
The suspect, who was arrested under the Terrorism Act, had reached for a four-foot (1.2-metre) sword upon being challenged by unarmed police officers after deliberately driving at them outside the royal palace.
Police said the man, who comes from Luton some 30 miles (50 km) north of London, had repeatedly shouted "Allahu akbar" (God is greatest) and was incapacitated with CS gas.
In an earlier statement, they said that searches were continuing in the Luton area and that they believed it was a "lone wolf" attack.
In Britain, 35 people have been killed in three jihadist attacks in London and Manchester since March.
Security measures in the British capital were stepped up to protect the hundred of thousands of revellers expected to flock to the Notting Hill Carnival, Europe's biggest street festival, which kicked off Sunday.
At a briefing ahead of the two-day event, police said it had no intelligence to suggest it could be the target of a terror attack, and said the number of police officers on site would be the same as last year.
But it also said that more than 650 people were arrested in the three weeks leading up to festival -- compared with 300 last year -- and that large quantities of knives and weapons were recovered.
Other measures put in place include weapons and liquid checks -- to prevent acid attacks -- and the use of facial recognition technology.
Friday's assault in London came just two hours after a knifeman attacked patrolling soldiers in Brussels in what authorities said was an "attempted terrorist murder".
Belgian prosecutors said the attacker yelled "Allahu akbar" (God is greatest) when he rushed at the soldiers from behind and struck them with a knife, prompting one of them to open fire.
The assailant -- a Belgian national of Somali origin born in 1987 -- was shot and died shortly afterwards in hospital, a prosecutors' statement said.
Granted Belgian nationality in 2015 after arriving in the country in 2004, he was not known for any terror-related activities, though he had an assault and battery charge from February on his record, authorities confirmed.
Police later raided his home in Bruges, in northwest Belgium.
One of the soldiers was slightly hurt in the attack which Brussels Mayor Philippe Close said had been carried out by a "lone individual".
Islamic State jihadists claimed responsibility for the attack on Saturday, saying on its propaganda outlet Amaq that "the perpetrator of the stabbing operation in Brussels is one of the soldiers of the Islamic State".
The two attacks came as much of Europe is on high alert following a string of deadly assaults over the past two years.
Last week, Spain was hit by twin vehicle attacks -- on Las Ramblas in Barcelona and in the seaside resort of Cambrils -- which left 16 dead and around 120 wounded.
The latest victim, a 51-year-old German woman, died on Sunday morning "after being treated in a critical condition in hospital," authorities said in a statement.
Two people were also killed in a stabbing spree on August 18 in the Finnish city of Turku.
Four men are still in custody for what is being treated as the country's first terror attack.