BISHKEK: Turmoil in Kyrgyzstan offers an ideal breeding ground for militancy in the Muslim region north of Afghanistan and the government must act quickly to curb any further violence, a UN envoy said.

Kyrgyzstan's ethnically divided south has been turbulent since a revolt in April toppled its president, Kurmanbek Bakiyev, and brought an interim government to power.

Russia and the West fear that instability in the ex-Soviet republic, which lies on a major drug trafficking route out of Afghanistan, could produce a safe haven to militants, particularly in the over-populated Ferghana valley.

"There is a threat of extremism in Ferghana valley and, more broadly, in Central Asia as a whole, in the sense that Central Asia borders Afghanistan," United Nations Special Envoy Miroslav Jenca told Reuters in an interview late on Wednesday.

"There are various extremist organizations ... And of course in these circumstances they are finding a fertile ground to fulfill their plans."

At least 191 people have been killed since June 10 in Kyrgyzstan's south in an outburst of ethnic violence between its two main ethnic groups, Kyrgyz and Uzbeks.

The violence has subsided in the last few days in a country where Russia and the United States have military air bases.

Up to 100,000 people have fled their homes and set up camps in Ferghana valley where Kyrgyzstan borders Uzbekistan.

Humanitarian aid has been flowing to the south but observers say it is not reaching many neighborhoods that have barricaded themselves in fear of further violence.

Muslim extremism is rare in Central Asia, a secular region ruled from Moscow until the Soviet Union's collapse in 1991.

But deepening problems such as poverty, illiteracy and people's growing frustration with their governments have made them more susceptible to Islamist ideas, emboldening radical groups to gain strength in Central Asia.

Those include the Islamic Movement of Uzbekistan and the less radical Hizb ut-Tahrir group but there have been no signs of increased militant activity since the April revolt.

The new leadership plans to hold a referendum on June 27 to vote on constitutional changes. Some officials have suggested Kyrgyzstan delay the poll until the situation stabilizes.

"If they (elections) are organized incorrectly then of course that would lead to big problems," Jenca said.

"The government has to assess whether it can organize the referendum in a way that would be legitimate, so it could be recognized."

Some 400,000 people have been displaced by ethnic violence in southern Kyrgyzstan, the United Nations announced Thursday, dramatically increasing the official estimate of a refugee crisis that has left throngs of desperate, fearful people without enough food and water in grim camps along the Uzbek border.

UN Humanitarian Office spokeswoman Elisabeth Byrs said an estimated 300,000 people have been driven from their homes but remain inside Kyrgyzstan. She said there are now also about 100,000 refugees in neighboring Uzbekistan. The last official estimate of refugees who fled the country was 75,000. No number of internally displaced has been available.

Ethnic Uzbeks in camps along the Uzbekistan side of the border told Associated Press reporters Thursday that they were fearful of returning to their homes. Many on the Kyrgyzstan side said they had been prevented from doing so by the authorities, and were awaiting their chance to leave the country for the camps.

A few parts of the south have been all but purged of the ethnic Uzbeks. In other areas, hundreds who hadn't fled have piled up old cars on the streets, barricading themselves into their neighborhoods.

In Britain, media reports said one of Bakiyev's sons had sought political asylum.

Maxim Bakiyev fled to Britain after Kyrgyz prosecutors put him on a wanted listed for allegedly avoiding almost $80 million in taxes.

The Home Office says the 32-year-old was questioned by officials when he flew into Farnborough Airport near London on a private plane Sunday without the necessary documents to enter the UK.

Britain's domestic news agency Press Association reports that Bakiyev is seeking asylum. The Home Office said it cannot comment on an ongoing asylum application.