NAIVASHA, Kenya — Army helicopters strafed crowds with machine-gun fire and police struggled to separate rival gangs yesterday as Kenya endured yet more violence. About 100 people have been killed since Saturday, bringing the number of deaths in the wave of tribal bloodshed since last month’s disputed election toward 900.

With vital roads blocked and tourists staying away, Kenya’s economy is suffering. Chaos in East Africa’s richest and best-developed country threatens the entire region. Near the tourist town of Naivasha, about 600 terrified people cowered inside a small police outpost. They were from the Luo tribe, as is the opposition leader, Raila Odinga. Outside were about 600 men armed with machetes from the Kikuyu tribe of President Kibaki.

At first, Kikuyus were the main victims of the violence as Luos and other smaller tribes, notably the Kalenjin, sought revenge for Mr. Kibaki’s victory in what they believe was a rigged election. Now Kikuyus are striking back.

Many of the Luo refugees had been driven from their homes during the weekend. Now, with only one armed policeman to protect them, they faced murder at the hands of the Kikuyu mob.

Unable to offer protection, police summoned three army helicopters. These swept low over the Kikuyu crowd, firing bursts from their machine guns. This spread panic, forcing the crowd to disperse. The pilots seem to have been firing not to kill but to intimidate and scatter the mob. They do not appear to have inflicted any casualties.

The fighting has brought a host of grievances to the fore. Kikuyus are blamed for taking over land in western Kenya, which has historically been farmed by the Luos and Kalenjins. Thousands of Kikuyu families have been displaced across the West.

Now some Kikuyus are striking back by trying to clear other tribes from their heartland in central Kenya. “They have sent our people out of the west, so we will now send them away from here,” said Christmas Kariuki, a 25-year-old Kikuyu, who boasted that he had burned down houses owned by Luos in Naivasha.

Meanwhile, Kenya’s economy is suffering. “With every day that passes, the economy is being hit from all sides, it’s devastating,” a Nairobi economist, Robert Shaw, said. “What started as a short-term shock we could recover from fairly swiftly is now something which is forcing businesses to make major decisions, and they’re not decisions which will be good for the future of Kenya.”

[In stark contrast to the bloodshed enveloping Naivasha, the area is normally best known for the peaceful industry of flower-growing. A third of Europe’s cut flowers come from Kenya, and the Naivasha region is at the heart of the business.

Four-fifths of the blooms are roses, and a quarter of those end up in Britain. The country also exports planeloads of packaged salads and green beans to Europe each day.

Tens of thousands of people are employed on the farms around the lake, which are so large that they have drawn enough water from it to lower the levels in recent years.

But with Valentine’s Day approaching, the violence means that deliveries could be under threat. Moving blooms thousands of miles so that they are still fresh when they arrive in Britain requires a precise and delicate operation.

Convoys usually leave the nurseries every few hours to take the produce to the airport, but now roads are sometimes blocked and some workers cannot get to their farms.

“It has greatly affected the industry,” said Martin ole Kamwaro, the corporate affairs manager for Shah Agencies, which exports 450 million stems every year.

Another grower, who did not want to be named, was concerned that overseas buyers would turn to other sources for February 14, the most lucrative day of the year for florists.

Flowers and tourism are Kenya’s two biggest foreign exchange earners, bringing in a combined $1.8 billion a year. But hotels and game parks are empty of visitors, and tourism leaders say the sector is “effectively dead” for this financial quarter.

Businesses in Uganda, Sudan, Rwanda, and Congo are also suffering as Kenya, east Africa’s financial hub, heads toward shutdown.]