Kyrgyzstan accused Tajikistan of breaking a ceasefire by firing on homes on Saturday and said 33 of its people have been killed in the deadliest border clashes between the countries since their independence from the Soviet Union.
The ceasefire was agreed on Thursday just hours after heavy fighting erupted on the Central Asian countries' long-contested border.
But Kyrgyzstan's national security committee said Saturday that Tajikistan's military had "opened fire on dwellings" in the Leilik district of Kyrgyzstan's southwestern Batken region, which borders Tajikistan.
The security committee said that villagers had been evacuated from the houses before the shooting began at 0645 GMT on Saturday.
In a previous release, Kyrgyzstan had accused Tajikistan of blocking a strategic road connecting a Kyrgyz territory to the rest of the country.
Kyrgyzstan also declared Saturday and Sunday days of mourning, while the health ministry announced that its death toll had risen from 31 to 33.
Since breaking out on Thursday, the violence has left more than a hundred Kyrgyz injured and over 30 properties destroyed, Kyrgyzstan said.
Tajikistan, a closed authoritarian state, has not officially acknowledged any deaths or damages from the conflict and did not immediately confirm that fighting had resumed.
Clashes between communities over land and water along the border are regular occurrences, with border guards often getting involved, however this week's violence was by far the most serious during the pair's 30 years of independence.
Kyrgyz authorities had said on Friday evening that fighting had finally stopped, after a ceasefire agreement that was reached on Thursday evening failed to stop intermittent shooting during the day.
Tensions had appeared to cool after talks between the presidents and national security chiefs of the two countries.
Kyrgyzstan President Sadyr Japarov and his Tajik counterpart Emomali Rakhmon spoke by telephone Friday, Japarov's press service said, and agreed to meet "in the second half of May".
Tajikistan's state information agency also published news of the call, confirming Rakhmon had invited Japarov to visit Tajikistan.
Neighbouring Uzbekistan and Russia, which maintains bases in both countries, have offered to mediate the conflict.
Border disagreements between the three countries that share the fertile Fergana Valley -- Kyrgyzstan, Tajikistan and Uzbekistan -- stem from demarcations made during the Soviet era.
The knotting, twisting frontiers left several communities with restricted access to their home countries.