"I can't say there is any breakthrough," Chief U.S. Negotiator Christopher Hill told reporters Wednesday evening.

The sticking point was how to verify the nuclear program of the Democratic People's Republic of Korea(DPRK).

Under an agreement reached at the six-party talks in February 2007, the DPRK agreed to abandon all nuclear weapons and programs. It also promised to declare all its nuclear programs and facilities by the end of 2007. In return, DPRK would get diplomatic and economic incentives.

The six parties agreed to a disarmament schedule in October 2007. The DPRK said it slowed down that process because of sluggish economic compensation.

When the new round of talks started Monday, China put together the views of all parties in a verification draft.

Describing Wednesday as "a tough, long day," Hill said everyone tried to discuss the Chinese draft but had difficulty getting consensus to move forward.

"It's not trending in the right direction. In terms of coming up with a verification agreement, we don't seem to be narrowing differences," Assistant U.S. Secretary of State Hill said. "I'm going to report to Washington."

There were extensive one-on-one meetings going on Wednesday, including one between Hill and his DPRK counterpart Kim Kye Gwan.

"I had a bilateral meeting earlier today with DPRK. Let me just say we had gone into many details, it's a difficult meeting," Hill said.

Although China had said the talks would last three days, envoys said they would extend their stay in Beijing to continue negotiations, which also include the Republic of Korea(ROK), Russia and Japan.

By last night, no party had said how long the talks would go on.

The process to denuclearize the Korean Peninsula started in 2003.