The two small, poor landlocked countries have accused each other of resuming fighting in a disputed area, despite a ceasefire agreement.
In a statement, the Kyrgyz border service said its forces continued to repel Tajik attacks.
“On the Tajik side, the shelling of positions on the Kyrgyz side continues, and in some areas intense fighting is taking place,” he added.
The Kyrgyz Health Ministry later said 24 citizens had been killed and 87 injured, Russian news agency Interfax reported. He did not specify how many of the victims belonged to the army.
Kamchybek Tashiev, the head of the Kyrgyz state committee on national security, was quoted by Russian news agency RIA as saying military casualties had been high.
“The situation is difficult and as to what will happen tomorrow, no one can give any guarantees,” he said.
The Kyrgyz Ministry of Emergency Situations said more than 136,000 civilians had been evacuated from the conflict zone, Interfax reported.
Earlier in the day, Kyrgyz President Sadyr Japarov and his Tajik counterpart Emomali Rakhmon agreed to order a ceasefire and troop withdrawal at a regional summit in Uzbekistan, Japarov’s office said.
Kyrgyzstan has reported fighting in its southern province of Batken, which borders Tajikistan’s northern Sughd region and includes a Tajik enclave, Vorukh. The same region is famous for its complex political and ethnic geography and became the scene of similar hostilities last year, which also nearly led to war.
Clashes over the poorly demarcated border are frequent, but generally defuse quickly.
Both countries host Russian military bases. Earlier Friday, Moscow called for a cessation of hostilities.
The clashes come at a time when Russian troops are fighting in Ukraine and a new ceasefire appears to have been reached between the former Soviet states, Armenia and Azerbaijan.
Kyrgyzstan said Tajik forces using tanks, armored personnel carriers and mortars entered at least one Kyrgyz village and shelled the airport in the Kyrgyz town of Batken and adjacent areas.
In turn, Tajikistan accused Kyrgyz forces of shelling an outpost and seven villages with “heavy weapons”.
Temur Umarov, a fellow at the Carnegie Endowment for International Peace, said the remote villages at the center of the dispute were not economically significant, but both sides had given it overblown political significance.
Umarov said the two governments had come to rely on what he called “populist and nationalist rhetoric” that made a territory swap aimed at ending the conflict impossible.
Another Central Asia analyst, Alexander Knyazev, said the parties had shown no willingness to resolve the conflict peacefully and mutual territorial claims had prompted aggressive attitudes at all levels.
He said only third-party peacekeepers could prevent further conflict by establishing a demilitarized zone.