China's first aircraft carrier officially entered service Tuesday, amid a worsening territorial dispute with Japan and regional concerns over Beijing's rapidly modernizing navy.

The defense ministry said in a statement that the Soviet-built aircraft carrier, named Liaoning after China's northeast province, is an important step in “raising the overall fighting capacity” of its naval forces.

The 300-meter ship, purchased from Ukraine in 1998, was delivered and commissioned to the People's Liberation Army (PLA) at a ceremony in the port city of Dalian, where the vessel was refitted.

The move comes as China is embroiled in a major diplomatic dispute with Japan over islands in the East China Sea, as well as disputes with Vietnam and the Philippines over oil and gas exploration in the South China Sea.

Yang Yi, a rear admiral and former director of the Institute for Strategic Studies at the PLA's National Defense University, said the carrier will be “mainly responsible for scientific research and training missions.”

Writing in the official China Daily, Yang deflected international criticism of China's expansion of its naval forces. He said “it is natural that China should have its own aircraft carrier,” arguing that all major world powers already own similar vessels.

Yang said the introduction of the carrier will not change what he called Beijing's “defensive” military posture, but noted that China has “vast sea areas and huge maritime rights and interests that it needs to protect.”

China, the last permanent member of the United Nations Security Council to own an aircraft carrier, is also reportedly developing domestically built carriers.

The news also comes amid increased suspicion between the United States and China about each other's influence across the Asia-Pacific region.

Washington has expressed concern at China's increasing maritime assertiveness, while Beijing fears that the U.S. is trying to contain it with its recently adopted military “pivot” toward the region.