Spanish police detained one of Europe's most wanted fugitive Islamic State (IS) fighters in the southern town of Almeria, the government said.
The Egyptian man, who has fought in Syria and Iraq, was hiding in an apartment with two other people who were also arrested and were being identified by police, the interior ministry said in a statement late on Tuesday.
A European security source said the man arrested was Abdel Majed Abdel Bary. "This is a significant arrest," the source said.
Bary has appeared in gory propaganda pictures of IS crimes, the ministry said.
"The detained man spent several years in the Syria-Iraq area and presents peculiar personality features such as an extremely violent criminal profile which caught the attention of police and intelligence services in Europe," the statement added.
The three suspects had come via North Africa and were keeping a low profile during Spain's coronavirus lockdown, exiting the apartment one-by-one and wearing protective masks.
A prominent IS foreign fighter, Bary was stripped of his British citizenship because of his links with the violent group, The Guardian newspaper reported.
Police are eager to intercept many of the dozens of Spanish Muslims who left for Syria and Iraq to fight alongside IS and may now want to perpetrate attacks on home soil such as the killing of 16 people in Barcelona in 2017.