TAIPEI - Taiwan's defence minister said on June 18 that they have a "grasp" of the situation after pictures appeared online of a Chinese nuclear submarine surfacing in the sensitive Taiwan Strait near Taiwanese fishermen.

The narrow strait that separates Taiwan from China is a frequent source of tension. Taiwan reports Chinese warplanes and warships operating there on a daily basis, as Beijing seeks to assert its sovereignty claims against the democratically governed island.

Taiwanese media published the pictures of the surfaced craft, which appears to be a nuclear-armed Jin class ballistic missile submarine, taken by a Taiwanese fishing boat in the strait as dawn broke on June 18, about 200km from Taiwan's western coast.

Asked about the submarine, Taiwan Defence Minister Wellington Koo said they have a “grasp” of the intelligence situation, but declined to say how they were monitoring it or give details.

China's defence ministry did not immediately respond to a request for comment.

Military experts say the strategic waters off Taiwan's southwestern shores, where the largely shallow Taiwan Strait descends in depth, provide submarines a location for an ambush, making it a hot spot for militaries including China, Taiwan and the United States.

Ballistic missile submarines are not designed to attack ships, but to launch ballistic missiles at targets on land.

Taiwan's fleet of P-3C Orion anti-submarine aircraft are based at the Pingtung air base in southern Taiwan, giving easy access to the southern part of the strait.

Taiwan has complained in recent years that China has been using so-called grey zone warfare designed to exhaust a foe without resorting to open combat, such as flying surveillance balloons over the island.

"We must be fully alert to China's continued military harassment...