Four Kyrgyz servicemen reported wounded while Tajikistan said there were casualties among its civilians and border guards.
Casualties have been reported after Kyrgyz and Tajik border guards exchanged fire amid a standoff over a blocked road, in the latest clash between the former Soviet neighbours following a similar violent incident last year that killed dozens.
The Batken provincial government in Kyrgyzstan said four servicemen have been wounded following the clash on Thursday, according to local news website 24.kg.
Tajikistan said there were casualties among its civilians and border guards, but provided no figures. A Tajik security source said one person was killed and eleven wounded.
The border between the two countries, both of which host Russian military bases and are closely allied with Moscow, is poorly demarcated.
The Secretary General of the Russia-led Collective Security Treaty Organisation (CSTO), Stanislav Zas, called for an immediate ceasefire at the border, RIA news agency reported.
It said Zas has held phone talks with senior security officials from Kyrgyzstan and Tajikistan.
â€œThe armed confrontation at the Tajik-Kyrgyz border should be immediately stopped,â€ he was quoted as saying by the news agency.
â€œI am confident that the leadership of both CSTO member states will find mutually acceptable ways to resolve this complex border issue.â€
He also said that the CSTO, of which both countries are members, stood ready to help resolve the conflict.
Kyrgyz authorities said Tajik citizens had blocked a road between the provincial centre Batken and the Kyrgyz village of Isfana.
Border guards on both sides managed to get the road unblocked, but then fighting broke out.
The Kyrgyz authorities said later in a separate statement that the two sides agreed a ceasefire around midnight but fighting resumed 10 minutes later.
Tajikistanâ€™s border guard service said its servicemen defended Tajik civilians and it was the Kyrgyz side that opened fire first.
Kyrgyzstanâ€™s national security committee said late on Thursday that two rounds of telephone talks had yet to produce a ceasefire as of 17:00 GMT.
â€œMoreover, (Tajikistan) continues to push heavy military equipment and personnel towards the border,â€ said the statement that cited Kyrgyzstanâ€™s border service head Ularbek Sharsheyev.
At least 49 people were killed in fighting between the two countries last April which escalated from a similar border clash and ignited fears of a wider conflict.