BRUSSELS, Sept 7 (Reuters) - Belgium’s justice minister had not been aware that three of his friends had urinated against a police vehicle during a party at his house, he told parliament on Thursday, and also denied joking about it afterwards.

Belgium has been rocked by what media have dubbed “pipigate” after news outlets published security camera images showing three of Vincent Van Quickenborne’s guests peeing against the van of police assigned to protect the minister’s residence.

Opposition politicians and police unions have also expressed outrage over footage in which Van Quickenborne appears to mimic his guests’ actions and joking about it at the end of the party for his 50th birthday.

At a parliament hearing, Van Quickenborne apologised and said he had not been aware of the incident the night it happened.

“I am ashamed that people I invited at my house peed against a police van, not once, but three times. It is disgusting, especially considering why the van is there,” he said.

Van Quickenborne has round-the-clock protection following a failed attempt to kidnap him last year.

He denied CCTV footage showed him mocking the incident later that night as he stood outside with one guest.

Van Quickenborne said he had no access to police video, but in parliament he played footage of cameras at his house.

“Some say these images show me in the act of mimicking the act of peeing. The person I was accompanying thinks … it is an air guitar solo …I admit I play air guitar some times … It is possible, I honestly do not know,” he said.

He added that prosecutors have opened an investigation.

Opposition politicians blasted Van Quickenborne.

“You have given a whole new dimension to the concept of the Belgian joke,” said opposition party N-VA’s Yngvild Ingels