Tajikistan began joint antiterror drills with China on October 20 near the border with Afghanistan as part of Beijing's drive to boost security in the region.
Tajikistan's Defense Ministry said the exercises would last until October 24 and involve at least 10,000 troops as well as military vehicles and helicopters.
Tajik authorities said last month that China would be building infrastructure to increase security on the 1,300-kilometer border between Tajikistan and Afghanistan, which is a haven for drug traffickers.
China and Tajikistan entered into an antiterror alliance with Pakistan and Afghanistan earlier this year.
Security issues in former Soviet Central Asia, a region that borders China's restive Xinjiang province, were once the exclusive preserve of Russia.
But China has dramatically increased its presence in the region and a suicide attack against the Chinese Embassy in Kyrgyzstan in August highlighted Beijing's security concerns.
Kyrgyz authorities blamed the attack, which injured three people and resulted in the attacker's death, on radicals from the Uyghur community, a mostly Muslim minority from Xinjiang.
The U.S. security footprint in the region has shrunk since Uzbekistan and Kyrgyzstan ended agreements for bases used in U.S. operations in Afghanistan.
Based on reporting by AFP and RFE/RL's Tajik Service