The United States and Russia, both operating military air bases in the strategic Muslim nation, are concerned that continued turmoil in Kyrgyzstan would spread to other parts of Central Asia, a vast former Soviet region north of Afghanistan.
Assistant Secretary of State Robert Blake was in Kyrgyzstan to meet its interim leadership and visit the turbulent south.
The government says as many as 2,000 Uzbeks and Kyrgyz may have been killed in several days of ethnic violence last week. The UN says an estimated 1 million people were affected.
In remarks posted on the State Department website, US Secretary of State Hillary Clinton said Kurmanbek Bakiyev, Kyrgyzstan's president who was toppled in a revolt in April, may be to blame.
"Certainly, the ouster of President Bakiyev some months ago left behind those who were still his loyalists and very much against the provisional government," she said.
"There certainly have been allegations of instigation that have to be taken seriously."
Bakiyev, now in exile in the ex-Soviet republic of Belarus, has denied any involvement in the events.
Interim leader Roza Otunbayeva, who became leader after the April uprising, has struggled to assert control in the shattered south where Uzbek neighbouhoods have barricaded themselves against Kyrgyz parts in a tense standoff.
She said Bakiyev loyalists, seeking to avenge their April expulsion, are trying to destabilise Kyrgyzstan ahead of a crucial referendum on a new constitution on June 27.
"I think we will be able to prevent any further outbursts," she told Reuters ahead of talks with Blake. "God help us stay this way."
The violence has triggered a wave of refugees, and around 400,000 people are now crammed into squalid camps on either side of the sun-parched Kyrgyz-Uzbek border, many without access to clean water, food and medicine.
Blake visited the camps on the Uzbek side on Friday and described the situation as a humanitarian crisis.
The continued presence of Uzbek barricades has added to simmering tensions between the two communities and slowed the delivery of humanitarian aid that has flown into the region from the United States, Russia and other countries.
Locals in the devastated city of Osh say government troops had joined with marauding gangs during the violence and human rights groups have called for an international probe.
"Amnesty International urges the (Kyrgyz) interim government to immediately react to allegations of collusion of security forces and to send a clear signal that any human rights violations will be prosecuted," Amnesty said in a statement.
In Kyrgyzstan, a complicated patchwork of clans and tribes, Bakiyev's departure triggered fierce competition for control over businesses in a country lying on a major drug-trafficking route out of Afghanistan.
Historically there has been a strong rivalry between Uzbeks and Kyrgyz but many observers say Bakiyev loyalists who stayed behind are playing on ethnic divisions to regain strength.
Uzbek President Islam Karimov spoke to Clinton by telephone on Friday and also accused "outside" elements in the unrest.
"Neither Uzbeks nor Kyrgyz are to blame for this," Karimov was quoted as saying by the official Uza news agency. "These disruptive actions were organized and managed from outside."
