Neighbouring Uzbekistan said Monday that up to 80,000 ethnic Uzbeks, mostly women and children, had fled the fighting and were being housed in hastily set-up camps along the border. Rights groups warned of a looming humanitarian crisis.
Ashton said it was "very important" that all parties "move forward in the way they were planning to do to try and sort out a stable government".
The provisional government has struggled to impose order since coming to power during deadly riots that ousted Kurmanbek Bakiyev in April.
Foreign leaders have since warned of the risk of civil war in the strategic state, which hosts both a US airbase outside the capital Bishkek, that is vital to its operations in Afghanistan, and Russian bases.
Several days of clashes in Osh have left at least 117 dead and 1,000 wounded, according to an official toll. Some estimates have said 100,000 people have crossed the border into Uzbekistan.
The Kremlin agreed to send humanitarian aid but has so far said conditions are not in place for any involvement of Russian forces in restoring order.
Russia leads a regional security body, the Collective Security Treaty Organisation (CSTO), grouping ex-Soviet republics in central Asia that is reportedly considering deployment of a rapid-reaction force to the region.
Meanwhile, shocked residents in Osh have said violence would have repercussions for generations to come.
Intermittent gunfire was heard on Monday while further to the north, in the city of Jalalabad, the violence was reportedly still in full swing.