Sources, however, said China has heightened its activity in the Indian Ocean which constantly monitored by India. The increase in patrolling could also be for anti-piracy operations in the Gulf of Aden and Arabian Sea and to protect cargo ships.
The presence of a Chinese submarine in the Indian Ocean region has nothing to do with stand-off between the Indian and Chinese troops along the border in Sikkim, Sources told news agency IANS.
They confirmed the presence of a conventional Chinese submarine in the Indian Ocean region for a while.
The Indian Navy, too, said "the submarine's presence has nothing to do with the present situation and it has been present in the Indian Ocean for a while now".
"Usually, Chinese submarines have three-month long deployment in the Indian ocean. This is routine," a Navy official said.
According to IANS sources, this is the same Yuan-class submarine that was "picked up" by Indian Navy's Poseidon-8I long-range maritime patrol aircraft as soon as it crossed the Malacca Strait on April 19-20.
The submarine of China's People's Liberation Army Navy's (PLAN) anti-piracy fleet had sought permission to dock at a Sri Lankan harbour in May but Sri Lanka declined it.
The submarine then headed towards Karachi and was reported to have docked there.
A recent report from Pentagon also confirmed that China continued to send submarines to the Indian Ocean in 2016. The report said "it appeared to be in support of its counter-piracy patrols".