The head of an election watchdog in Azerbaijan has been arrested.

Our correspondent says Anar Mammadli was questioned by police in Baku on December 16 on charges including tax evasion and illegal business activity.

He has been ordered held for three months in pre-trial detention.

Mammadli is the chairman of the Election Monitoring and Democracy Studies Center.

The center monitored elections in Azerbaijan this fall and exposed widespread irregularities and fraud during balloting and vote counting.

Mammadli is a leading figure of civil society in Azerbaijan. Authorities have been trying for years to silence him and his election watchdog, his supporters say.

Mammadli's arrest comes a day ahead of a visit to Baku by the EU Energy Commissioner Gunther Oettinger and the British Foreign Secretary William Hague.

On December 17, the two are scheduled to attend the signing of a multi-billion-dollar gas pipeline deal.