Violent fans who disrupted a Bucharest derby at the weekend had smuggled explosives in their underwear to manufacture flares in the stadium, the head of the city's riot police said on Monday.

Fans of arch-rivals Steaua and Dinamo threw flares and smoke bombs at each other and on to the pitch, as Saturday's match was halted three times in the opening 12 minutes.

'The fans hid gun powder and different other materials in their underwear and carried them into the stands,' police general Olimpiodor Antonescu told Reuters.

'So, they needed a few minutes to manufacture their flares and bombs and then throw them onto the pitch.' .