* Co-CEO asked to face questions by police after speech
* Gaming companies face uncertain regulatory climate
* Shares close down 4.2 percent
By Robert-Jan Bartunek and Keith Weir
BRUSSELS/LONDON, Nov 13 (Reuters) - Belgian prosecutors have questioned one of online gaming group bwin.party's co-chief executives, taking advantage of his presence in the country to request an interview on Tuesday.
Bwin.party said Norbert Teufelberger was cooperating fully and had not been arrested. The world's largest listed online gaming group is in a dispute with Belgium over licences, and access to three of its websites has been blocked this year.
A spokeswoman for the public prosecutor said bwin.party, whose products include online poker and casino games and betting on sports events, had previously been asked to come to Brussels, and had not done so.
Authorities then acted after they became aware Teufelberger would be in Brussels on Tuesday, and plainclothes police called at a conference on "Responsible Gambling", where Teufelberger was the main speaker, to ask him to answers questions.
The company said it had only become aware authorities wanted to question Teufelberger when they received a letter in Flemish at their offices in Gibraltar on Tuesday and had not had time to let him know. Bwin.party shares closed down 4.15 percent.
The case brings into sharp focus the risks faced by companies in the growing online gaming sector which operate in countries where regulations are either unclear or restrictive.
Blocking access to bwin.party websites was costing the company 700,000 euros ($890,000) gaming revenue each month, a spokesman said. Bwin.party says rules in Belgium do not comply with European law.
Teufelberger, an Austrian, had been speaking at a conference organised by the European Gaming & Betting Association. Police asked Teufelberger to attend questioning after the conference at around 1300 GMT, EGBA Secretary General Sigrid Ligne said.
Bwin.party, formed following the merger of bwin and PartyGaming in March 2011, is listed in London.