Port Harcourt - Some 2 000 women protesting against the conduct of elections in Rivers state were teargassed on Monday as they tried to register their complaints with electoral officials, AFP reporters said.
Armed police and soldiers prevented the women, from the All Progressives Congress (APC) and all dressed in black, from entering the electoral commission offices in the state capital, Port Harcourt.
The APC alleges that the ruling Peoples Democratic Party (PDP) and election officials rigged the presidential and parliamentary election, which was held on Saturday and Sunday.
"What happened today was unprecedented," said APC women leader Victoria Nyeche, a local lawmaker.
"The police teargassed and injured some of us during a peaceful protest at INEC (Independent National Electoral Commission).
"All we want is a fresh election because what happened on Saturday was a fraud."
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AFP reporters at the INEC offices, after the crowd dispersed early on Monday and reassembled at the state government headquarters, said the air was thick with the smell and taste of teargas.
Rivers state in the oil-producing Delta is seen as a key battleground for the presidential election, in which APC candidate Muhammadu Buhari is fighting the PDP's President Goodluck Jonathan.
At the last election in 2011, the state was won by the PDP but governor Rotimi Amaechi switched to the APC two years later and there has been bad blood between the two parties ever since.
The PDP has dismissed the APC's allegations and calls for the election to be rescheduled in the state, saying it was "the behaviour of bad losers".
Elections chief Attahiru Jega confirmed having received a letter from the opposition calling for a re-run and promised a "thorough investigation".
"There are many alleged cases of malpractice and we certainly pay a lot of attention to... it and if any of our staff are involved, we will will apply appropriate sanctions," he said on Sunday.