Aid agencies handling the emergency meanwhile reported fresh allegations of atrocities from the survivors.
Bodies littered the streets of the southern Kyrgyzstan city of Osh where fresh gunfire rang out, and more fighting was reported in the nearby city of Jalalabad.
Scores are reported killed in four days of clashes. With estimates of up to 100,000 people already inside Uzbekistan, the Central Asian state's Deputy Prime Minister Abdullah Aripov said the border would be shut, despite pleas from aid groups and the UN to leave it open.
"Today we will stop accepting refugees from the Kyrgyz side because we have no place to accommodate them and no capacity to cope with them," he said.
Uzbekistan needed international humanitarian aid to cope, he said. "If we have the ability to help them and to treat them of course we will open the border" again, he added.
Aripov said Uzbekistan had registered 45,000 adults from Kyrgyzstan, while another official said there were 65,000 adults in Uzbekistan's Andijan region alone. The UN's refugee agency said it was sending aid for 75,000.
Ethnic Uzbeks and Tajiks have flooded into Uzbekistan in the four days of bloodshed around Osh and Jalalabad, which has left at least 170 dead and 1,762 wounded, the health ministry said Tuesday.
The violence exploded Friday in Osh when ethnic Kyrgyz gangs began attacking the shops and homes of ethnic Uzbeks, igniting tensions between the two dominant groups in the region that have simmered for a generation.
The unrest comes barely two months after President Kurmanbek Bakiyev was overthrown in a popular uprising. Bakiyev's stronghold is in southern Kyrgyzstan.
Ethnic Uzbeks said many more had been killed and accused government forces of helping Kyrgyz mobs in their deadly rampage. Charred corpses lay unattended in a burned out ethnic Uzbek shop in Osh and the streets were strewn with shell cases and wrecked cars.
Intermittent gunfire could be heard and new violence was reported further north in Jalalabad.
UN High Commissioner for Human Rights Navi Pillay urged Kyrgyz authorities to act firmly. "It seems indiscriminate killings, including of children, and rapes have been taking place on the basis of ethnicity."
The violence appeared to have been "orchestrated, targeted and well-planned," she added. She urged both Uzbekistan and Tajikistan to accept refugees.
Officials of the International Committee of the Red Cross (ICRC) said they too had received reports of atrocities.
Over the border in Uzbekistan, the ICRC's deputy head there, Francois Blancy, said he had seen about 40 men with gunshot wounds among the refugees.
"Some spoke of homes burning with children inside and the ICRC is clearly worried about the accounts we're hearing of extremely brutal violence."
Kyrgyz news agency AKIPress said 2,000 people had gathered in the main square in Jalalabad and cafes and stores were ablaze. It also said 150 to 200 youths were marching around threatening to shoot Uzbeks.
In Osh, Uzbek men with makeshift weapons stood guard outside their homes while women and children cowered in basements. Dildor Dzhumabayev, a 38-year-old ethnic Uzbek, said people were gunned down by armed personnel carriers that were used to clear the way for mobs on the streets.
The crisis has prompted growing international alarm, with both the United States and Russia having military bases near the capital of the former Soviet republic.
China and Turkey sent planes to pick up their nationals in Kyrgyzstan. The UN Security Council meanwhile condemned the violence, calling Monday for "calm, a return of rule of law and order and a peaceful resolution of differences."
Russian President Dmitry Medvedev said "the current situation in Kyrgyzstan is intolerable".
Over the weekend however, he ruled out sending Moscow's troops in to restore order, which Kyrgyzstan's interim president, Roza Otunbayeva had requested, but said Russia would send aid. But the Russian-led regional body, the Collective Security Treaty Organisation (CSTO), held emergency talks on Monday on the deployment of a special force to the region.
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