The move comes after several days of protests by opposition supporters.

The opposition members arrested belong to the Rally of Repubicans (RDR) party, led by Alassane Ouattara. He is the main challenger to president Henri Konon Bedie in presidential elections scheduled for next year.

The imprisoned - who are due to appear in court next week - include the secretary general of party, Henriette Diabate, the deputy secretary general, Amadou Gon Coulibaly, and the leader of the party's parliamentary group, N'Golo Goulibaly.

Mr Ouattara's citizenship was withdrawn

The United States has called for their release, saying it is very concerned that the arrests appear to be aimed at stifling the opposition.

Mr Ouattara has also called for the immediate release of his party colleagues.

At the same time, he announced his intention to appeal against the government's decision to cancel his certificate of nationality -- a move which could prevent him standing in next year's presidential contest.

Government regret

After the arrests at a rally on Wednesday, the RDR said it feared a return to one-party rule.

"These incidents attest to the fact that the government is determined at all cost to violate all public freedoms and human rights," RDR spokesman Aly Coulibaly said during a visit to Paris.

President Bedie: Accused of undermining democracy

"We have gone back to the single party system, the party state and a doctrinaire approach to government," Mr Coulibaly said, in remarks broadcast on Gabonese radio.

In the same news programme, Ivorian Communication Minister Danielle Boni-Claverie expressed regret over the day's events.

But he insisted that "these arrests were not arrests in the true sense of the word, because they took place at the demonstration venues and, especially, because a rather overzealous police officer manhandled people".

The current crisis began when an Ivorian nationality certificate issued to RDR leader Alassane Ouattara was cancelled.

Eligibility

Mr Ouattara's supporters say President Henri Konan Bedie's government is unnecessarily harassing their leader because of the increasing threat he poses in next year's ballot.

Mr Ouattera, who has held senior positions in the International Monetary Fund, is currently outside the country.

President Bedie says Mr Ouattara's father is from neighbouring Burkina Faso and he is therefore not eligible to stand.

Mr Ouattara insists that both his parents were born in Ivory Coast and says that he has the documents to prove it.

Forgery pressure

A judge, Zorro Ballo, who issued the Ivorian nationality certificate to Mr Ouattara, says he had come under political pressure to say it was a forgery.

He said senior officials in the Ministry of Justice accused him of being a rebel judge and of having been promised something by the opposition leader in return for the Ivorian nationality document.

He insists that he has acted strictly within the law and that he has now revealed the political pressure on him because he feels his professional integrity is under threat.