South Korea, the United States and Japan have agreed to lower the bar on conditions for resuming long-stalled nuclear talks with North Korea, a diplomatic source with knowledge of the matter said Monday, saying Pyongyang must show its sincerity through the same pledges it made in a scuttled aid-for-disarmament deal with the U.S. more than two years ago.

The agreement was reached at the trilateral talks in Washington last week among top nuclear envoys of South Korea, the U.S. and Japan. They listed several conditions, which were originally set by the U.S. and North Korea in February 2012, as steps the North should take before the resumption of the six-party talks, the source said on condition of anonymity.

Under the so-called "Leap Day" deal between Washington and Pyongyang, North Korea agreed to suspend nuclear and long-range missile tests and allow international inspectors to monitor its nuclear sites in exchange for food aid.

The deal fell apart when North Korea launched a long-range rocket two months later and conducted its third nuclear test a year later.

Subsequently, South Korea, the U.S. and Japan had called on the North to take steps beyond what it agreed to in the "Leap Day" deal before resumption of the talks.

The move to relax the conditions for talks comes amid threats by North Korea to carry out a "new form" of nuclear test ahead of visits by U.S. President Barack Obama to South Korea and Japan later this month.

"Two principles have been set before resumption of the six-party talks can take place. The first is to make practical progress in denuclearizing North Korea and the second is to prevent the North from sophisticating its nuclear capability," the source said.

"Under the principles, there are various ways to resume the six-party talks. But, North Korea must meet conditions set under the Feb. 29 agreement," the source said, referring to the deal between the U.S. and North Korea.

After the trilateral talks in Washington, South Korea's chief nuclear envoy, Hwang Joon-kook, visited Beijing last week, during which he discussed the issue with his Chinese counterpart Wu Dawei.

Wu is now on a week-long visit to the U.S. for talks with his U.S. counterpart, Glyn Davies.

"China agrees on the need for North Korea to meet preconditions ahead of the six-party talks, but it insists that the level of preconditions should be reasonable," said the source, who also is involved in the talks between Hwang and Wu.

But North Korea has shown no signs of declaring a moratorium on nuclear and missile tests or allowing back international nuclear inspectors, the source said, adding that the "ball is now in the North Korean court."

The six-party talks involving the two Koreas, the U.S., China, Japan and Russia have been dormant since late 2008.

Meanwhile, China asked South Korea to refrain from holding large-scale military drills with the U.S. on the Korean Peninsula during the Friday talks between Hwang and Wu, according to the source.

In response, South Korea insisted that the annual drills with the U.S. are defensive in nature, the source said. (Yonhap)