By Ange Aboa and Tim Cocks
ABIDJAN (Reuters) - Forces loyal to Ivory Coast presidential claimant Alassane Ouattara advanced on Tuesday to within 200 km (120 miles) of the two main coastal cities in an intensifying offensive against incumbent Laurent Gbagbo.
The United Nations said forces loyal to Gbagbo opened fire on civilians in the commercial capital of Abidjan on Monday, killing about 10. Gbagbo's government dismissed the report and declined to comment, saying Abidjan was "impregnable."
A violent dispute over last November's presidential election that U.N.-certified results showed Ouattara won, but which Gbagbo refuses to concede, has rekindled the civil war it was meant to end. Heavy fighting has erupted in Abidjan and now across much of a north-south ceasefire line.
Witnesses and fighters from both sides said on Tuesday that the former rebels, who have controlled northern Ivory Coast since the civil war of 2002-3, had seized the western towns of Daloa and Duekoue in overnight fighting.
From there, they marched on Issia, another cocoa hub around 50 km to the south of Daloa, seizing it with apparent ease. "The (former) rebels entered Issia without any fighting. They are controlling the town," said Issouf Camara, a local cocoa trader.
If they continue south, the road will take them on to the major cocoa exporting port of San Pedro, about 200 km away.
"These places seem to be falling quickly. You would have thought they had better forces, fighters that wouldn't give up," said a diplomat following the situation.
The western area they now control produces about 600,000 tons of cocoa a year, half of Ivory Coast's output. San Pedro ships out about that amount each year.
Pro-Ouattara forces also made progress in the east, near the Ghana border. They took Bondoukou in the northeast before marching 200 km south to, and through, Abengourou unopposed, residents said, leaving them some 200 km northeast of Abidjan.
Heavy fighting also flared in the northern Abidjan suburb of Abobo, which is under control of anti-Gbagbo fighters.
Up to one million Ivorians have now fled fighting in Abidjan alone, according to the U.N. refugee agency. Others have been uprooted across the country and at least 112,000 have crossed into Liberia to the west.
Cocoa futures were lower on Tuesday, down 3.3 percent in London at 1346 GMT, as the market closely watched conflict which has pushed them to 30-year highs in past months.
Gbagbo's government spokesman Ahoua Don Mello denied a claim by the U.N. mission that pro-Gbagbo forces opened fire on civilians in the neighborhood of Williamsville, killing 10.
The mission has also accused Gbagbo's forces of using heavy weapons against civilians in Abidjan, prompting France to propose a Security Council resolution banning their use.
"We haven't used any heavy weapons to attack the civilian population ... what they say does not reflect the reality," Don Mello said. "We are doing our own investigations."
He said Ouattara's men would be unable to march on Abidjan.
"Their efforts to infiltrate other parts of Abidjan besides Abobo have been failures. Abidjan is impregnable," he said.
Unlike the last war, when French peacekeepers stepped in at Duekoue to stop the rebels advancing on San Pedro, world powers are this time furious with Gbabgo for torpedoing the peace process by rejecting the election results.
All recognize Ouattara as president and diplomats say they are therefore unlikely to hinder the former rebels' advance.
But the humanitarian toll is mounting.
International Organization for Migration (IOM) spokesman Jean-Philippe Chauzy told a news briefing in Geneva that "some 20,000 Ivoirians and West Africans migrants (in Duekoue) had found refuge in an overcrowded Catholic mission with little or no access to shelter, food, water and health facilities."
Ouattara remains holed up in a lagoon-side Abidjan hotel.
The U.N. report of more civilians killed adds to a tally of 462 confirmed deaths since the crisis begin.
The world body is also investigating allegations that 200 African nationals -- from Mali, Burkina Faso, Senegal, Guinea and Togo -- were killed near Guiglo, southwest of Duekoue.
State television has been whipping up hatred by accusing West African foreigners of being behind the rebellion.
(Additional reporting by Loucoumane Coulibaly; Writing by Tim Cocks and David Lewis; editing by Elizabeth Piper)