The State Department said Thursday its special envoy for implementing U.N.-mandated sanctions against North Korea will return to Asia next week for more talks on tightening economic curbs against Pyongyang. Ambassador Philip Goldberg said he thinks efforts to put an economic squeeze on North Korea after its nuclear test in May are beginning to have an effect.

The appointment of Philip Goldberg to promote implementation of the June 12 U.N. Security Council resolution, tightening sanctions after the nuclear test, reflects the high priority the Obama administration has placed on the issue.

The career diplomat, most recently U.S. ambassador to Bolivia, says he thinks the new international pressure, aimed at forcing North Korea back to nuclear negotiations, is beginning to be felt in Pyongyang.

Goldberg spoke at a news briefing where he announced he will lead an interagency team of senior U.S. officials to Singapore, Thailand, South Korea and Japan starting next week, his second Asia mission since being named to the post in late June.

Resolution 1874 tightened sanctions mandated by the Security Council after North Korea's first nuclear test in 2006, and included a call on U.N. member countries to inspect North Korea's maritime and air cargo suspected of being related to weapons proliferation.

Last month, a North Korean freighter, the Kang Nam-One, suspected of carrying illicit weapons technology destined for Burma, turned back for home after it was reported to be under surveillance by U.S. and other naval forces.

Goldberg told reporters the apparent decision to recall the vessel is one, early, indication the new sanctions push is being noticed by North Korean authorities.

"The North Korean ship was coming down toward Southeast Asia and eventually turned around," he said.  "It was after quite a bit of diplomatic activity, after a lot of consultation.  So I think it's had an effect.  But it's going to take time for this to all work. And we're committed to a steady process of using this as one route, while still offering a greater conversation about returning to those irreversible steps on denuclearization."

Earlier this week, Indian authorities detained and searched a North Korean cargo vessel after it reportedly had engaged in suspicious activity, but later released the ship and its crew, having found no evidence of illegal cargo.

Goldberg indicated the inspection issue would be a key part of his talks with officials of maritime powers Singapore and Thailand, and that meetings in South Korea and Japan would focus on efforts to resume the Chinese-sponsored six-nation talks on the North Korean nuclear program.

The envoy stressed that U.S.-led efforts to tighten economic pressure were aimed at stifling North Korea's once-lucrative business in nuclear and missile technology proliferation, and not at increasing economic hardships for the North Korean people.

He also said the Obama administration, which penalized another North Korean bank Wednesday for allegedly supporting proliferation activities, is enforcing the existing U.N. sanctions and not creating new ones, and is keeping the door open to a return by Pyongyang to the nuclear talks.

Goldberg, who has already visited China, Malaysia and Russia in his new capacity, said he plans another trip to China soon, perhaps before the end of this month.