Almost 30 people have been reported killed and dozens injured in clashes on the Kyrgyzstan-Tajikistan border.
Fighting regularly flares up between the two former Soviet states, whose border has been disputed since the collapse of the USSR.
A fresh skirmish which began earlier in the week continued on Friday, despite the two countries agreeing a ceasefire.
Both sides blame the other for beginning the violence and breaching the ceasefire.
Some 24 people in Kyrgyzstan have so far been killed, the Kyrgyz health ministry said on Friday.
Earlier reports from Tajikistan said at least three people had been killed there.
Almost 20,000 people have fled their homes to avoid the violence, a regional branch of the Red Cross reported.
The conflict has renewed fears of an all-out war between the two countries.
The dispute flared up on Wednesday with at least two people killed in three separate incidents.
Kyrgyz border guards accused Tajikistan of taking positions on part of the border that has not been demarcated, while Tajikistan said Kyrgyz guards had opened fire without provocation.
The countries share a 1,000-km (600-mile) border, more than a third of which is disputed.
Russia - which has close ties with both countries - has offered to mediate, calling for "urgent" measures to stop the violence on Friday.
A ceasefire took effect from 16:00 local time (10:00 GMT), but Kyrgyzstan said two of its villages were later shelled.
It accused its neighbour of using tanks and armoured personnel carriers.
In turn, Tajikistan accused Kyrgyz forces of shelling an outpost and seven villages with "heavy weaponry".