China’s new missile is being called the “Guam killer” because it could attack a U.S. military base in the Pacific Ocean with a nuclear weapon.

Defense Ministry spokesperson Wu Qian said the DF-26 intermediate range ballistic missile was now in service and could carry conventional and nuclear warheads to attack targets at land or sea. It has a range of up to 4,000 kilometers, or 2,500 miles, meaning it could hit important U.S. installations on the island of Guam, or other military bases in the region. Wu said China would not launch a nuclear strike against an opponent unless it was an act of defense, the Associated Press reported.

This is the first time the DF-26 missile has been operational. China previously showed it off during a 2015 military parade marking the 70th anniversary of World War II ending.

The big reveal this week is the latest sign that China is working to upgrade its massive military with new fighter planes, aircraft carriers and advanced missiles amid growing tensions in the Korean Peninsula and South China Sea.

“China’s military modernization is targeting capabilities with the potential to degrade core U.S. military-technological advantages,” a Defense Department report warned Congress last year. “The DF-26, which debuted publicly last year, is capable of conducting intermediate precision strikes against ground targets that could include U.S. bases on Guam.”

Roughly 7,000 U.S. military personnel are stationed at Naval Base Guam and Andersen Air Force Base. The island is also home to four nuclear-powered fast attack submarines.

U.S. leaders aren’t the only ones concerned about China’s military growth. China’s air force held this week what it called “combat military drills” exercises near democratic Taiwan with reconnaissance planes and H-6K bombers. Ma Xiaoguang, spokesman for China’s Taiwan Affairs Office, said the People’s Liberation Army was sending an “extremely clear” message.

“We have the resolute will, full confidence and sufficient ability to foil any form of Taiwan independence separatist plots and moves and to defend the country’s sovereignty and territorial integrity,” Ma said.

“If Taiwan independence forces continue to do as they please, we will take further steps,” he added.