Initial indications after Congo's constitutional referendum point to the "Yes" vote taking a significant early lead. But, opposition leaders who called for a "No" say the vote is being rigged while a member of their campaign is still being held by security services.

Polling stations closed late Monday after the Democratic Republic of Congo held its first independent election in more than 40 years.

Initial ballot count results point to the "Yes" vote establishing a significant lead, with more than 70 percent of the 650,000 votes from across the country.

But the U.N. radio station in Congo, which has been monitoring the process and providing results, said the figures can only be used as indicators because they represent just three percent of the votes cast.

Congo's poll about whether to accept or reject a post-war constitution has been seen by many as a dry run for local, parliamentary and presidential elections, which must be held by mid-2006.

The elections are the cornerstone of a string of peace deals that were concluded in 2003 and officially ended Congo's last war, a five-year conflict that sucked in six neighboring countries and has killed about four million people.

Congo's past is marked with dictatorship, war, and chaos. But millions in the mineral-rich country, as well as the international community backing the peace process, have pinned their hopes on the polls providing a fresh start.

But opposition leaders who called for a "No" vote are crying foul. They say the vote is being rigged for "Yes", while the population had voted "No".

They also complained that Theodore Ngoy, their spokesman who, who was arrested during a meeting last week is still being held by the authorities.

U.N. officials confirmed that Mr. Ngoy had been held since last Friday. And they said they are hoping to clarify his status as his arrest appears to be arbitrary.