"The United States believes that North Korea should refrain from testing missiles," Gordon Johndroe, a White House spokesman, said in a statement. "This kind of activity is not constructive."

He added: "North Korea should focus on the denuclearization of the Korean peninsula and deliver a complete and correct declaration of all its nuclear weapons programs, and nuclear proliferation activities and to complete the agreed disablement."

North Korea test-fired three or four missiles into the Yellow Sea on Friday, according to the Yonhap news agency, raising the stakes in its nuclear disputes with South Korea and the United States.

They were described as Russian-designed Styx ship-to-ship missiles with a range of 46 kilometers (29 miles).

There were several similar launches last summer.

State Department spokesman Sean McCormack suggested that North Korea might be taking its eye off its commitments to the six-party negotiations that also involve China, the United States, South Korea, Japan, and Russia.

"In terms of the short-range missile test, I understand they are not a violation of the missile moratorium" for long-range missiles that North Korean leader Kim Jong-Il declared in 1999, McCormack told reporters.

"That said, we would urge to them to -- rather than engaging in launching short-range missiles -- to direct their energies towards more productive channels, focus on producing a declaration, focus on meeting their commitments," he said.

North Korea last year agreed to disable its main atomic plants at Yongbyon and declare all its nuclear programs and materials by the end of 2007.

The US-supervised disablement has been going ahead but Washington and Pyongyang are at odds over the declaration.

The North says it submitted the declaration last November. The United States says it has not fully accounted for a suspected uranium enrichment program and for allegations of nuclear proliferation to Syria.

"We're beyond the deadline the parties have set for themselves," McCormack said when asked about prospects for a new deadline.

"We'd like to see this move forward as quickly as possible, but you've also heard the secretary (of state Condoleezza Rice) say she hasn't circled any dates on the calendar in that regard."

He added there was still life left in the diplomatic process.

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