A senior politician from Hungary's ruling party, who quit as an MEP on Sunday, said he had been present at a house party broken up by Brussels police for breaching lockdown rules.

Jozsef Szajer, a leading light in Prime Minister Viktor Orban's ruling conservative Fidesz party, apologised for any wrongdoing in a statement released today.

"I regret to have broken the lockdown rules, that was irresponsible of me, and I will accept the sanctions that result," he said.

The statement was quoted in an identical way by at least four prominent Hungarian news web sites. Reuters was unable to download the original text.

Police intervened because Friday's party violated lockdown rules, which in Belgium forbid any gathering of more than four people in a closed space, Belgian prosecutors said.

Prosecutors said police detained about 20 people in an apartment, in a building in which there is a bar, in central Brussels.

"A report was ... drawn up for S.J. for violation of the narcotics legislation," Sarah Durant, spokeswoman for Brussels prosecutors, said in a statement.

She said criminal proceedings could only be brought after a waiver of diplomatic or parliamentary immunity of those involved.

Hungarian news site Telex.hu cited prosecutors as saying that S.J. was Mr Szajer. Reuters was unable to reach Mr Szajer for comment.

In his statement, Mr Szajer denied taking drugs and said he had offered police to take a drugs test at the scene.

"The police said they had found ecstasy pills. They were not mine, I know nothing of who put them there and how. I told that to police," he said in his statement.

Mr Szajer, a prominent member of Hungary's political elite for decades and who authored the main draft of Hungary's new constitution in 2011, resigned on Sunday, effective at the end of the year, citing unspecified moral reasons.