It also dropped its request for a peacekeeping force, saying violence was waning. Russia has said it will not send troops to the country.
Southern Kyrgyzstan has been hit by days of rioting which has seen tens of thousands of ethnic Uzbeks flee towards the border with Uzbekistan.
Eyewitnesses in the cities of Osh and Jalalabad have reported seeing rows of houses burnt down, and bodies lying in the streets.
The office of the UN high commissioner for human rights has told reporters in Geneva there is evidence that the violence has been co-ordinated. It says there is evidence of indiscriminate killings - including the murders of children - and rapes.
The government hopes the referendum will approve reforms that will pave the way for parliamentary-style elections in October.
It was called after the ousting of President Kurmanbek Bakiyev in April.
Interim leader Roza Otunbayeva told a news conference: "We will fight to the last to ensure that the referendum takes place."
The United Nations and European Union had urged Kyrgyzstan not to allow the ethnic unrest to derail the referendum and elections.
At the weekend, Ms Otunbayeva appealed to Russian President Dmitry Medvedev to send military forces to Kyrgyzstan, saying that the situation in the south of the country was out of control.
But on Tuesday she told reporters: "There is not a need to send peacekeeping forces. We hope to deal with this situation with our own forces."
Her comments came as the Organisation for Security and Co-operation in Europe said it was deeply concerned about the ethnic violence, and warned that there was a risk of it spilling over into other countries.
The clashes are the worst ethnic violence to hit southern Kyrgyzstan since 1990, when several hundred people were killed. Kyrgyzstan was then part of the Soviet Union, which sent in troops to quell the unrest.
Kyrgyzstan's interim government, which came to power after violent protests overthrew the previous administration, has been quick to blame supporters of ousted President Bakiyev.
Mr Bakiyev, who now lives in exile in Belarus, still has widespread support in the south, but he has denied whipping up tensions.
The UN has called for the setting up of a "humanitarian corridor" in Kyrgyzstan to help people affected by the fighting.
Uzbek refugees say that armoured vehicles in Osh drove through streets in Uzbek neighbourhoods, shooting at civilians and clearing the way for gangs following behind.