Police and border agents from Kyrgyzstan and Tajikistan are hunting suspected militants along their shared border in Central Asia.
The search comes after four suspected members of the banned Islamic Movement of Uzbekistan were killed on Sunday in the northern Tajik city of Isfara.
Several other suspected militants escaped after a gunfight with police.
Four other suspected militants were arrested in Vorukh, a Tajik enclave in southern Kyrgyzstan, officials said.
The joint Tajik-Kyrgyz security operation was launched after a group of suspected militants shot their way across the border last week.
Tajikistan's interior ministry spokesman said the search for those who escaped the shootout in Isfara was continuing.
"The security forces fired back and killed four Islamists; another one surrendered and was detained," the spokesman, Tokhir Normatov, told Reuters news agency.
The Tajik authorities believe that the alleged militants are members of the Islamic Movement of Uzbekistan (IMU), a militant group with links to the Taliban.
The group has been blamed by the authorities of other Central Asian states for a number of incidents over the summer in the Ferghana Valley, a strategic strip of land shared by Tajikistan, Kyrgyzstan and Uzbekistan.
There has been growing concern that militants affiliated to the IMU, who have fought alongside the Taliban in Afghanistan and Pakistan's tribal regions, may be returning to the Ferghana Valley.