The Chinese Ministry of Defense announced Thursday that China and Russia will launch a joint military drill in the South China Sea in September, a move observers say shows the two countries have formed a "semi-alliance" in the face of an increasingly assertive US.

"This is a routine drill between two military forces aimed at strengthening the developing China-Russia strategic cooperative partnership," said Yang Yujun, spokesperson for the Ministry of National Defense during a regular monthly press conference in Beijing on Thursday.

Even though Yang said the exercise is not directed against third parties, experts consider that the choice of location and the timing show the drill is aimed specifically at countering the increasing US military presence in the Asia-Pacific.

Shi Yinhong, director of the Center for American Studies at the Renmin University of China, told the Global Times that "due to the great pressure Russia receives from the West in Europe, Moscow is becoming more motivated to having deeper strategic cooperation with Beijing at this moment. The drill is an obvious example in the military area."

Shi believes there is no denying that the US is the major strategic rival of both China and Russia. Under pressure from the US, China and Russia are moving their bilateral relationship to a semi-alliance level, Shi said.

Reinforce global stability

China and Russia are both permanent members of the UN Security Council with veto powers. The two countries have cooperated on many international issues in the past, including the Syria crisis and nuclear issue in both Iran and North Korea.

On June 26, Chinese President Xi Jinping and Russian President Vladimir Putin signed a joint statement in Beijing which aims to reinforce global strategic stability. Experts believe that the military drill in the South China Sea in September is an action based on that statement.

The joint statement makes clear that China and Russia want strategic stability. As both countries believe the US is encroaching on the geopolitical balance in the region, it is only natural for the two nations to stand together, Shi said.

Song Zhongping, a Beijing-based military expert, said the drill's location also shows a strong signal to countries that are trying to get involved in the South China Sea issue militarily.

In 2015, the China-Russia joint military drill was in the Sea of Japan; in 2014, in the East China Sea.

"It's very clear that both countries will pick a hot spot region to launch a drill … this year China and Russia both agreed that to have the drill in the South China Sea has a specific political aim," Song said

Timing coincidental

In September 2016, the G20 Summit will be held in Hangzhou, Zhejiang Province, while the ASEAN Summit will also take place in Vientiane Laos, but experts stressed that the timing of the drill has nothing to do with these events.

Rather, said Song, it is based on the season and weather conditions rather than diplomatic reasons. In September, conditions in the South China Sea are ideal for the exercises.

Shi believes that "Chinese and Russian military forces will avoid the G20 Summit due to the sensitiveness of the timing."

On the specific military aims of the drill, Song considers that the two navies will focus on traditional naval battle craft, such as anti-submarine and anti-aircraft missions, but the drill will be bigger in scale than last year's.

Infrastructure on South China Sea islands might also be used during the drill, Song said.

"The Yongxing Island airport in the Xisha Islands can be used for military aircraft, but others in the Nansha Islands are not ready yet," he noted.