Kyrgyzstan and Tajikistan on Friday accused each other of using heavy weaponry such as tanks and mortars in an escalating border conflict that has killed at least three people and injured 27 since fighting broke out two days ago.

The border guard said Kyrgyz forces were returning fire on Friday morning, as clashes took place along the length of the border, adding that Tajik forces were using tanks, armoured personnel carriers, and mortars. More than one-third of the 1,000km (600-mile) frontier remains disputed.

In turn, Tajikistan accused Kyrgyz forces of shelling one of its outposts and seven villages with “heavy weaponry”. A civilian was killed and three injured, authorities in the Tajik city of Isfara said.

Kyrgyz President Sadyr Japarov and Tajik President Emomali Rahmon are both attending a regional security summit in Uzbekistan and appeared, together with a number of other leaders, in a group photo for the Shanghai Cooperation Organisation (SCO) at a gala dinner on Thursday.