Croatian police arrested former Interior Minister Josip Boljkovac Wednesday and accused the 90-year-old of ordering the execution of 21 prisoners at the end of World War Two.

The arrest is the first move against former senior officials of the 1945-1990 communist regime since Croatia declared independence from socialist Yugoslavia.

Police spokesman Krunoslav Borovec confirmed the arrest and charges against Boljkovac who turns 91 this month and remains in detention.

Conservative and right-wing parties welcomed the arrest, carried out by special police wearing balaclavas, saying all war crimes must be investigated.

Liberal and centre-left parties dismissed it as an electoral manoeuvre by the ruling conservative HDZ, who have been hit by corruption scandals, to woo right-wing voters ahead of a December 4 general election.

This is just a manoeuvre to improve their ratings. In 1990, all these HDZ members stood quietly in front of Boljkovac, without uttering a word about his past, said Damir Kajin, leader of a small party that is part of a centre-left coalition tipped to win the December vote.

Boljkovac, who denies the charges, was a close ally of the first Croatian president, Franjo Tudjman, and his first interior minister. In 1945, he had headed the local branch of OZNA, a communist-era security service.

Police say Boljkovac had in 1945 ordered the arrest and execution of 21 civilians suspected of collaborating with Croatia's pro-Nazi Ustasha regime.

Unlike other former communist countries across Eastern Europe, Croatia never launched a large-scale investigation into the possible wrongdoings of communist-era leaders.

(Reporting by Zoran Radosavljevic; Editing by Robert Woodward)