BEIJING - China denied on Thursday that it had increased its troop presence on the border with North Korea after the murder of the estranged half-brother of North Korean leader Kim Jong Un in Malaysia.

Reports routinely circulate at times of heightened tension on the Korean peninsula of China sending troops to the border, which China always denies.

South Korean and US officials say the North Korean leader's half brother, Kim Jong Nam, was assassinated by North Korean agents. North Korea has not acknowledged his death.

Some Hong Kong media last week reported that China had sent more soldiers to the border after Kim was attacked at Kuala Lumpur airport on Feb. 13.

"As for the reports you mentioned of the People's Liberation Army increasing troops on the Chinese-North Korean border, they are totally baseless and completely fabricated," defence ministry spokesman Ren Guoqiang told a monthly news briefing.

Meanwhile, China's defence ministry said on Thursday it was aware of the presence of a US aircraft carrier strike group in the South China Sea and China respected freedom of navigation for all countries in the waters there.

The US navy said the strike group, including the Nimitz-class aircraft carrier the USS Carl Vinson, began "routine operations" in the South China Sea on Saturday amid growing tension with China over control of the disputed waterway.

Defence ministry spokesman Ren Guoqiang said China had a "grasp" of the situation regarding the carrier group in the South China Sea.

"China hopes the US earnestly respects the sovereignty and security concerns of countries in the region, and earnestly respects the efforts of countries in the region to maintain peace and stability in the South China Sea," Ren told a regular monthly news briefing. "Of course, we also respect freedom of navigation and overflight for all countries in the South China Sea in accordance with international law," he added.

The situation in the South China Sea was generally stable, Ren said.

"We hope the actions of the US side can contribute positive energy towards this good situation, and not the opposite."

Good military relations between the two countries are in interests of both, and well as of the region and the world, and China hoped the United States could meet China half way, strengthen communication and avoid misjudgement, Ren said.

Friction between the United States and China over trade and territory under US President Donald Trump have increased concern that the South China Sea could become a flashpoint.

China wrapped up its own naval exercises in the South China Sea late last week. War games involving its only aircraft carrier have unnerved neighbours with which it has long had rival claims in the waters. China lays claim to almost all of the resource-rich South China Sea, through which about $5 trillion worth of trade passes each year.

Brunei, Malaysia, the Philippines, Taiwan and Vietnam also claim parts of the waters that have rich fishing grounds, along with oil and gas deposits.

The United States has criticised China's construction of man-made islands and build-up of military facilities in the sea, and expressed concern they could be used to restrict free of movement.