Some 6,000 opposition supporters rallied in Baku on Saturday to protest strongman Ilham Aliyev's crushing victory in an election that observers said fell short of international standards.

Aliyev cruised to a third term that sees him extend his family's decades-long rule in the ex-Soviet state with some 85 percent of the vote in Wednesday's poll, far ahead of main challenger Jamil Hasanli on around 5.5 percent, according to the official results.

But observers from the Organisation for Security and Cooperation in Europe (OSCE) condemned the poll as "seriously flawed" and Aliyev's opponents said the vote was riddled with violations and should be annulled.

"Dictators who have stolen power have no place in Azerbaijan-- Ilham Aliyev must go and he will go," Hasanli told a cheering crowd.

"The results of the election must be cancelled and a new vote held," Hasanli said, as supporters chanted for Aliyev to resign.

The rally by the opposition-- which joined forces behind Hasanli at the polls in a rare show of unity-- was held on a football pitch in a residential area outside the city centre after being officially sanctioned by local authorities.

Any show of dissent is usually dealt with harshly in Azerbaijan, and the government has lashed out at accusations that the election was fixed.

Rights groups accused the authorities in the oil-rich state of an intense clampdown on criticism in the run-up to the polls, with scores of opponents jailed on charges the opposition say are trumped up.

Police briefly detained several protestors following scuffles after the rally, opposition activists said.

The 51-year-old Aliyev -- who took power in 2003 in a disputed election after the death of his father Heydar, a former KGB officer and Communist-era boss -- has a vice-like grip over most of the media in the Caspian sea nation.