London - British police investigating Friday's sword attack outside Buckingham Palace in London arrested a second man on Sunday, as authorities in Belgium, Finland and Spain probed their own terror attacks."The man was arrested on suspicion of being involved in the commission, preparation or instigation of terrorism at 10:15 (09:15 GMT) today and he has been taken into custody," a police statement said.It came hours after Islamic State jihadists claimed Friday's knife attack on patrolling soldiers in Brussels and as authorities in Spain revealed 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 sword upon being challenged by unarmed police officers after deliberately driving at them outside the world-famous landmark.'Allahu akbar' Police said the man, who comes from Luton some 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 searches were ongoing 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.The 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" 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, although 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 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". Europe on high alert 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 Cambris - 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.The Brussels attack happened near the Grand Place central square, where armed soldiers are on patrol because of the terror threat.Soldiers have been deployed at railway stations and landmark buildings in the Belgian capital since the November 2015 attacks on Paris, when investigators found the assailants had a clear link with Brussels.Patrols have been stepped up since suicide bombers struck Zaventem Airport and the Maalbeek metro station in March 2016, killing 32 people and wounding hundreds.The carnage in Paris, which left 130 people dead and hundreds wounded, was claimed, as were the Brussels bombings, by Islamic State.In June, a man who tried to bomb a Brussels Central train station was shot dead by a soldier.