Planes have begun delivering foreign aid after the violence which engulfed south Kyrgyzstan's ethnic Uzbeks.
UN refugee agency planes are landing in neighbouring Uzbekistan where some 75,000 people fled to safety before the country closed its borders.
Russian government planes have been arriving in the Kyrgyz capital Bishkek carrying food and blankets.
With at least 179 deaths reported, more than a quarter of a million people are said to have fled their homes.
The true number of casualties is unknown, as many of the dead were buried without relatives registering them as having been killed. A further 1,870 people are said to have been injured.
While there were no reports of heavy fighting between Kyrgyz and ethnic Uzbeks on Wednesday, ethnic Uzbeks in Osh threatened to blow up a city oil depot if they did not get guarantees of protection.
Kyrgyzstan's interim leaders have been struggling to impose their authority since coming to power after President Kurmanbek Bakiyev was overthrown in April.
Two UN refugee agency flights landed in the Uzbek city of Andijan carrying tents and other emergency supplies, the agency said. Four flights are to follow later this week.
The agency believes about 200,000 people are displaced within Kyrgyzstan while some 75,000 have sought safety in Uzbekistan.
"What is happening is already a tragedy and it could become a catastrophe," UN High Commissioner for Refugees Antonio Guterres told German radio.
Two Russian government cargo planes, each carrying 42 tonnes of aid including food and blankets, landed in Bishkek.
Pascale Meige Wagner, regional head of the International Committee of the Red Cross, said there were people still trapped in their homes, including people in need of medical care, and food was running out.
The World Food Programme says it has 3,000 tonnes of food, mainly wheat flour and oil, already in Kyrgyzstan.
It would be enough to feed 87,000 people for two months, but road deliveries are hazardous amid the unrest.
Talks have been under way in Osh between Kyrgyz officials and ethnic Uzbeks holding the oil depot, which stores most of the petrol distributed in the region.
One of the Uzbeks' representatives told the BBC they no longer trusted the government and Kyrgyz military, and were hoping for UN peacekeepers to intervene.
Officials in Jalalabad, which also saw violence, say a suspected organiser of the clashes has been detained.
They say there is strong evidence that allies of Mr Bakiyev fomented the unrest.
The UN has said it believed the initial violence was "orchestrated, targeted and well-planned".
Ms Wagner of the Red Cross said her team on the ground was unable to judge whether ethnicity was at the root of the violence.
"What is striking us is the level of brutality, I mean the willingness to harm and to kill, and this is really something that is extremely worrying for us," she told the BBC.
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.
A Kyrgyz government appeal for Russia to send in peacekeeping troops was rejected by Moscow.
Washington is sending its top Central Asia diplomat, Robert Blake, for meetings with officials in Bishkek on Friday and Saturday.
The clashes are the worst ethnic violence to hit southern Kyrgyzstan since the dying days of the USSR when several hundred people were killed.