South Korea proposed on Thursday working-level talks with North Korea regarding suspended operations at the joint Kaesong industrial zone, the same day the North celebrated the 81st anniversary of the foundation of the Korea People's Army (KPA) amid missile launch tensions.

South Korea's unification ministry spokesperson Kim Hyung-seok said an official offer has been made to the North to hold talks and provide humanitarian aid to South Korean workers in the joint industrial complex and the North should reply by Friday morning, adding that the South will have to take significant measures if the North refuses it.

Kim did not specify what measures the South is to take but analysts suggested the ultimatum indicated that the South is considering a permanent withdrawal from the zone.

"After the North suspended operations in the complex and denied requests to send food and supplies, withdrawal seems to be a reasonable option at the moment," Zhang Liangui, a professor at the Party School of the CPC Central Committee, told the Global Times.

The zone, formed in 2002, has been viewed as a symbol of inter-Korean conciliation.

As the tensions on the Korean Peninsula escalated after North Korea's nuclear test in February, Pyongyang decided on April 3 to block all South Korean access to Kaesong and later on April 9 pulled out its entire workforce of some 53,000 people and suspended operations.

"With no substantial change in the inter-Korean relations, the economic collaboration is very fragile," said Zhang.

Some 176 South Korean employees are still in Kaesong, a drastic drop from the usual number of around 850.

No missile was launched by North Korea despite earlier reports that it would likely take actions on the anniversary. The North has threatened to attack South Korea, Japan and the US after the new UN sanctions were imposed following its latest nuclear test in February.

The escalated tension has raised concerns in East Asian countries as well as the US.

General Martin Dempsey, chairman of the US Joint Chiefs of Staff, said Thursday in Japan that his troops are ready to act if North Korea turns its increasingly bellicose rhetoric into action.

China is considering holding a trilateral but informal dialogue with South Korea and the US and agreed to open a 24-hour hotline with the South for prompt policy consultations on North Korea, the Yonhap News Agency reported on Thursday.

"China has really started to feel anxious about what will happen on the Peninsula after carefully observing the situation for the past few months," said Zhang, "Beijing is, for the first time in decades, actively seeking measures to increase the consensus with Washington and Seoul on North Korea."

Agencies contributed to this story.