President Tsai Ing-wen confirmed Thursday that Taiwan’s Chief of the General Staff Shen Yi-ming was among those who died when a Black Hawk helicopter crashed in a mountainous area southeast of the capital Taipei during a routine flight.

Thirteen people—three crew members and 10 military officials—were aboard the helicopter when it crashed, The New York Times reported.

Tsai wrote on Facebook, “The safety of personnel is the first priority,” noting she had ordered “all units to do their best to search and ensure the safety” of those who survived the crash.

In a second post, Tsai confirmed Shen’s death. “Today is a sad day,” she wrote. “The National Army has several excellent generals and colleagues who lost their lives in the accident,” Tsai continued, including Shen who she described as “an excellent, capable general and loved chief.”

Tsai extended her “deepest condolences to the families of all the victims” and explained that the ministry of defense would provide full assistance to bereaved relatives.

The president also said she would make sure there was no negative impact on the island nation’s military readiness while the government oversaw rescue efforts and established the cause of the accident.

“The most important thing is that during this period, we should ensure the stability of the national army and maintain the sound of the national defense work, and do not be affected,” Tsai wrote.

Shen’s helicopter left the Songshan Airport in Taipei just before 8 a.m. local time, heading to a military base in Yilan County in northeastern Taiwan for a routine inspection, the Times reported.

Contact was lost with the aircraft at around 8:22 a.m., the BBC noted, when the helicopter made an emergency landing in the mountainous Wulai district in bad weather.

Early reports suggested that some of those aboard had survived the crash but were trapped in the wreckage.

The BBC cited the state-run Central News Agency as saying that the air force dispatched two more Black Hawk helicopters and around 80 soldiers to the crash site for a search and rescue operation.

The Black Hawk helicopters are among the American military equipment sold to the self-ruled island, to help it maintain independence from mainland China. Beijing considers Taiwan a wayward province and has vowed to bring it under Communist Party control, whether through diplomatic means or by force.

Taiwan is entering the final phase of its presidential election campaign, with the vote to be held on January 11. Tsai and her Democratic Progressive Party are currently ahead in the polls, leading main opponent Han Kuo-yu of the Kuomintang party.

Tsai had previously warned that Chinese military activity in the Strait of Taiwan is increasing and said last month that Beijing is attempting to influence the coming election.

The graphic below, provided by Statista, compares the military forces of China and Taiwan.

This article was updated to include an infographic.