China and Russia will start a joint counter-terrorism drill, known as Peace Mission 2013, on Saturday, less than one month after the two sides completed their largest-ever naval drill in the Sea of Japan.

Observers said this is the first time that the two countries have conducted so many drills in a short period of time and sent military forces from bases that are geographically so close to one another, indicating a high level of mutual trust.

The drill, which involves 1,500 soldiers, will be held in Chelyabinsk, in Russia's Ural Mountains region, from Saturday until Aug 15.

It will be the ninth time that the two countries have participated in bilateral or multilateral exercises since 2003, and the move comes two weeks after they held the Joint Sea 2013 naval drill in Peter the Great Gulf near Russia's Far East port city of Vladivostok.

Starting on Saturday morning, 646 Chinese soldiers from the Shenyang military division of the People's Liberation Army will be deployed by air and rail. They are expected to arrive in the drill areas by Aug 2, according to the military region.

It will be the first time that the military division, which is in northeastern China near the border with Russia, will participate in drills abroad, it said.

The move shows ever-growing mutual trust between the two sides, said Chen Xuehui, a Beijing-based military expert. "Traditionally, military forces that are geographically close are supposed to be each other's opponent in defense policies.

"Such cooperation is important given that forces near to each other usually face similar threats and conduct similar exercises in daily training," said Chen, adding that counter-terrorism has been a main subject of military cooperation under the framework of the Shanghai Cooperation Organization that groups China, Russia, Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan.

The deployment of troops will be followed by two phases of war planning and campaign drills.

According to the Ministry of National Defense, the Chinese troops will include a planning panel, a command, an infantry combat group, an air force combat group and a logistics group. They will be equipped with various models of armed vehicles, self-propelled guns, and fixed-wing and rotating-wing aircraft, including Z-9 and M-171 helicopters.

"The size of the drill is not much larger than those held before, but it's rare that the two countries hold two drills within a month," said Li Shuyin, a researcher on Central Asian and Russian military studies at the PLA Academy of Military Sciences.

"Both sides have been holding such drills regularly, further strengthening military ties, a key part of their comprehensive strategic partnership," Li said.

"And this does not target any third party," she said.

The first Peace Mission joint counter-terrorism drill involving the two countries was held 2005. Since then, the two countries have held similar drills every one or two years in China or Russia.