Xu Shichuang, 29, has been an inspection officer at Khunjerab for 10 years. He has learned to speak Urdu, the official language of Pakistan, to communicate better with Pakistani travelers.

"It's a tough job just to be at such high altitudes. I also have to make sure no drugs or weapons get pass me. I won't forgive myself if one bullet is smuggled in because that could cause someone's life," Xu said.

The station also stepped up searches for books or other material containing information on religious extremism, as its spread has led to more terrorist attacks in Xinjiang.

Xu watched an eagle hovering in the valley near the inspection station during his short break and took a deep breath to inhale as much of the precious thin air as possible.

As Xu returned to work, Lu Duobin, deputy head of the station, was having a meeting with Syed Akbar Rizvi, inspector of the Pakistani police's Khunjerab Security Force, whose logo is an ibex－a common animal in Khunjerab. Chinese inspection officers have also spotted snow leopards in nearby mountains.

They were discussing how to locate and return the Pakistani herdsmen's missing yaks that were likely to have wandered into China. Rizvi said the herdsman was worried because the yaks are valuable assets to the family.

"Exchanging missing yaks and sheep is actually one of our important jobs. We see it as illegal crossing too. It's an international diplomatic issue," Lu said firmly.

Of course, anti-terrorism cooperation is the two border forces' top priority, and sharing intelligence is critical, Rizvi said.

"As Chinese border defense forces are very strong at Khunjerab, we rarely see terrorist activities. Near the Pakistan and Afghanistan border the Taliban is still quite active, so we launched an attack in June and killed three main leaders in the area. Such information is important to China too," he said.

The KSF has a station about 1 km off the Khunjerab boundary marker. Sergeant Ashzaq Hussain has been working at Khunjerab for more than 10 years.

"The Chinese border defense officers are not just friends to us. We are brothers and so are Chinese and Pakistani people," Hussain said.

"We know the pain brought by terrorist attacks and we won't let terrorists or separatists enter China to ruin the lives of our brothers."

Contact the writer at cuijia@chidaily.com.cn