Secretary of State John Kerry said Friday it was too early to discuss cutting the number of US troops stationed in Asia and South Korea, amid increased tensions on the heavily guarded peninsula.

The warning came a day after Washington and Seoul agreed to delay transfer of the Pentagon's control of Korean troops in the event of war with the North. No new date was set to handover the powers.

The agreement, reached between Defense Secretary Chuck Hagel and his South Korean counterpart Han Min-Koo, serves as a "blueprint" for when Seoul takes wartime operational control of the combined forces, Kerry said.

In the event of war with North Korea, current plans call for an American military commander to lead the 28,500 US troops deployed in South Korea as well as that country's 640,000-strong force

Kerry insisted there could be no talk of withdrawing US troops until Pyongyang proves it is committed to rejoining six-party talks on ending its suspected nuclear program.

US troops have been stationed on the peninsula since the end of the Korean War in 1953.

Asked after meeting his South Korean counterpart Yun Byung-Se whether Washington would consider reducing its military presence in Asia if North Korea returned to negotiations, Kerry dismissed the idea.

"We remain open to dialogue with North Korea, but there is no value in talks just for the sake of talks," Kerry said.

"North Korea must demonstrate that it is serious about denuclearization, and we need to be certain that it is prepared to live up to its international obligations."

He stressed that "the mere entering into talks is not an invitation to take any actions regarding troops or anything else at this point.

"It would be way too premature to have any thought, or even discussion" along those lines, he said.

He also said Washington would not be issuing an apology to Pyongyang to secure the release of two Americans, Matthew Miller and Kenneth Bae, saying the two men were being held "inappropriately."

A third US citizen, Jeffrey Fowle, was suddenly freed earlier this week after six months in detention. The circumstances leading up to his surprise release have not been disclosed.

- Unification -

Yun said South Korea was awaiting a "clear stance" on Pyongyang's nuclear policy and "a halt to the sophistication of its nuclear weapons."

"All of this has to be real. It has to lead to real solutions," Yun said.

The two Koreas agreed to resume high-level talks during a surprise visit to the South by a top-ranking North Korean delegation earlier this month.

Seoul has proposed an October 30 start date, but the only response from Pyongyang so far has been to warn the talks might not happen at all.

Yun said recently Pyongyang has behaved erratically and that "what they speak and what they do seem to be inconsistent."

But he insisted that if the two Koreas can start high-level talks "I believe we can find a path to improvement of relationship for peace on the Korean Peninsula, as well as an environment conducive to unification."

"We are making various efforts to try and provide that kind of an environment."

Kerry also ruled out any idea of visiting the isolated country and meeting leader Kim Jong-Un in the near term. Washington and Pyongyang do not have diplomatic ties.