Jakarta. The Indonesian Military, or TNI, has raised combat alert for its forces stationed in the Natuna archipelago – in the south part of the disputed South China Sea – in response to Chinese vessels trespassing into Indonesia's exclusive economic zone, or the EEZ. 

"Our Navy and Air Force are armed and have been deployed to the North Natuna Sea," TNI spokesman Maj. Gen. Sisriadi said on Friday. 

The TNI has also deployed surveillance and early detection systems to ensure no more ships from China would trespass again.

The Foreign Affairs Ministry stated last week that Chinese vessels, including a coast guard boat, had entered Indonesian territory that the country had christened as the North Natuna Sea.

China has been claiming that the area part of its territory, bordered by its self-imposed nine-dash line.

"We are not only deploying ships, but also fighter jets. We are on full alert," Sisriadi said. 

The TNI said they have enough forces at the ready to handle a clash with the Chinese fleet. 

He said the TNI would also soon activate a Maritime Information Center to detect any movement by vessels violating Indonesia's sea borders.

"[The facility] will be able to detect and identify every ship that enters Indonesian waters," Sisriadi said.

Meanwhile, the Coordinating Minister for Political, Legal and Security Affairs Mahfud M.D. hosted a meeting on Thursday with related ministers and heads of state agencies to discuss the current situation in the North Natuna Sea. 

"The fact is Chinese vessels had violated the borders of the Indonesian EEZ [exclusive economic zone]," Foreign Ministry Retno Marsudi said after the meeting in Jakarta.

She said the North Natuna Sea is part of the Indonesian EEZ determined by the 1982 United Nations Convention for the Law of the Sea (UNCLOS), of which China is a party and thus should respect. 

"Indonesia will never recognize China's nine-dash line since it has no legal basis according to international law," Retno said.

The Foreign Affairs Ministry last week summoned China's ambassador to Indonesia to convey its official stance on the Natuna stand-off.

The combat preparations in the North Natuna Sea are being led by the commander of the Regional Defense First Command, Rear Adm. Yudo Margono, who departed for Natuna from Jakarta's Halim Perdanakusuma Air Force Base on Thursday. 

According to Yudo, Indonesia has sent three warships, one maritime surveillance plane and one Boeing airplane as reinforcements. Two more warships will join the operation soon.