BEIJING (Reuters) - China expressed "regret" on Monday that South Korea had extended its air defense zone to partially overlap with a similar zone declared by Beijing two weeks ago that has raised regional tensions.

China's declaration of an air defense identification zone in the East China Sea that includes islands at the heart of a territorial dispute with Japan has triggered protests from the United States and its close allies Japan and South Korea.

South Korea said on Sunday that its move to expand its own zone would not infringe on neighboring countries' sovereignty.

"China expresses regret over South Korea's expansion of its air defense identification zone," Foreign Ministry spokesman Hong Lei told reporters at a regular press briefing.

China had immediately conveyed its concerns to South Korea and requested that Seoul handles the matter "safely and cautiously", Hong said.

Hong said the zones, which overlap in an area that includes a submerged reef, called the Suyan Rock by China and Ieodo by South Korea, did not constitute territorial airspace.

"There currently does not exist a territorial dispute between China and South Korea on this issue," Hong said, but noted that the reef was situated in portions of both countries' exclusive economic zones.

"This can only be resolved through maritime negotiations," Hong said of the economic zone issue, which puts at stake rights to potential underwater oil and gas reserves.

South Korea objected to China's November 23 move as unacceptable because of the reef, which has a research station platform built atop it and is controlled by Seoul.

Under the Chinese zone's rules, all aircraft have to report flight plans to Chinese authorities, maintain radio contact and reply promptly to identification inquiries.

The extension of South Korea's zone, which was originally established by the U.S. Air Force in 1951 during the Korean War, will not apply any restrictions to the operation of commercial flights when it takes effect on December 15.

(Reporting by Michael Martina; Editing by Alex Richardson)