US group Human Rights Watch has accused Nigeria of torturing and killing several of its critics over the past two years and urged the Commonwealth to address the abuses at a summit later this week.
The organization accused Nigeria's government of cracking down on dissent in the run-up to April 2003 polls and of continued repression since then.
In a report ahead of the December 5th-8th Commonwealth summit in the capital Abuja, Human Rights Watch said abuses included the torture of people who had been opposed to a visit to Nigeria by US President George Bush in July.
Britain's Queen Elizabeth is due to open the Commonwealth meeting, and dissident groups have accused police of planning a clampdown ahead of her arrival.
"Foreign governments remained virtually silent about election violence in Nigeria, yet abuses during the Zimbabwe elections provoked widespread condemnation," Mr Peter Takirambudde, the head of Human Rights Watch's African division, said in a statement accompanying Tuesday's report.
"There is no excuse for Commonwealth leaders to turn a blind eye to human rights abuses in the very country where they are meeting."
The report said at least 100 people were killed during presidential, legislative and regional elections in April and May, which foreign observers said were marred by serious fraud.
At least a dozen people were killed by security forces during a general strike over fuel prices in June and July, Human Rights Watch said. It accused police of shooting into peaceful demonstrations in action "reminiscent of the military era".
Nigeria emerged from 15 years of army rule in 1999, when retired general Olusegun Obasanjo was voted in as president. Mr Obasanjo has often been accused of failing to rein in security forces since then.