Kyrgyzstan's interim leader Roza Otunbayeva has said the death toll in the country's worst ethnic violence in decades could be as high as 2,000.
Officials say at least 191 people were killed in fighting between Kyrgyz and ethnic Uzbeks around Osh and Jalalabad.
But Ms Otunbayeva told a Russian newspaper that the real toll could be "10 times the official figures".
Meanwhile, a US envoy in the region has called for an investigation into the unrest.
Central Asia envoy Robert Blake made the call while visiting refugees in camps in the Uzbek border city of Andijan on Friday.
About 400,000 people have fled their homes, with many ethnic Uzbeks crossing into Uzbekistan.
Mr Blake is due to travel later to the capital, Bishkek, for talks with Kyrgyz officials.
Ms Otunbayeva made the comments about the death toll in the Kommersant newspaper, saying that the real toll might never be known because of the custom of family burying loved ones as soon as possible.
She travelled to Osh on Friday for the first time since the violence.
Speaking in Osh's main square, Ms Otunbayeva said: "I came here to see, to speak with the people and hear first hand what happened here."
She rejected criticism of her interim government's handling of the crisis, adding: "We will do everything to rebuild this city."
The Kyrgyz government had earlier appealed to Russia to send in peacekeeping troops. But Moscow rejected the request, offering instead technical assistance to track those committing the violence.
The Red Cross (ICRC) has described the situation as an "immense crisis", with shortages of basic necessities.
The unrest last week came two months after the country's former president, Kurmanbek Bakiyev, was forced out of office.
Ms Otunbayeva's government has blamed the former leader for stoking the conflict.
Eyewitnesses say Kyrgyz mobs began attacking people in Uzbek areas of Osh and Jalalabad in the early hours of Friday last week.
About 300,000 people have fled their homes, while another 75,000-100,000 people - not counting children - are thought to have taken refuge in Uzbekistan.
The UN's health agency, the WHO, said up to a million people could be affected.
In the refugee camps in Uzbekistan, there are many reports of rape and severe beatings.
Some aid has begun to arrive in the region, but the ICRC says refugees are running short of basic supplies. At least 40,000 refugees were without shelter.
The organisation said insecurity and fear, combined with shortages of basic necessities like food, water, shelter and medicine, were putting a tremendous strain on communities, hospitals and families.
Kyrgyzstan's interim leaders have been struggling to impose their authority since coming to power after President Bakiyev was overthrown in April.
The government believes allies of Mr Bakiyev, who now lives in exile in Belarus, want to derail a national referendum on constitutional reform scheduled for 27 June.
But the government has said it will go ahead with the referendum despite the clashes.
Ethnic Uzbeks have largely supported the interim government, but Mr Bakiyev remains popular with many Kyrgyz in the south.