A pro-democracy protesters hold photos of detained Chinese artist Ai Weiwei during a protest to demand the release of the outspoken government critic, in Hong Kong, May 2. - AP File Photo

VIENNA: Austria has summoned China's ambassador to Vienna to protest the detention of artist Ai Weiwei, Foreign Minister Michael Spindelegger said on Tuesday.

“Even somebody who is critical of the regime should be allowed to express himself,” Spindelegger, who met with Ai during a trip to China in February, told journalists.

Spindelegger insisted Austria, which is seeking a seat on the United Nations Human Rights Council on May 20, would continue to push for the artist's release, noting: “We know that he remains in custody.” He did not say when the summons happened.

Austrian Chancellor Werner Faymann has made clear that he will raise the issue of Ai's detention on a visit to China later this week.

China has so far refused to say where Ai Weiwei is being kept after he was taken into custody in Beijing on April 3 as he tried to board a flight to Hong Kong.

During his encounter with Spindelegger in February, the artist had already spoken of the repressive measures taken against him.

According to Beijing, Ai is under investigation for unspecified “economic crimes.”