The United States on Wednesday criticized North Korea as "provocative" and urged restraint after it fired artillery shells near its disputed maritime border with South Korea.

"The declaration by North Korea of a no sail zone and the live firing of artillery are provocative actions and as such as not helpful," State Department spokesman Philip Crowley told reporters.

North Korea had declared two "no sail" zones near the disputed border and fired more than 80 shells despite warning shots by South Korea.

The US Defense Department called for restraint in the Korean peninsula, where the United States stations some 28,500 troops in the democratic South. The maritime border was the scene of deadly naval clashes in 1999 and 2002.

"Although this is a bilateral issue between the North and the South, we clearly are discouraging of any further acts of aggression which would in any way increase the tensions along this historically disputed boundary area," Pentagon press secretary Geoff Morrell told a news conference.

"We want to see everybody exercise restraint as they deal with this issue."

No one was hurt in the shelling, which some analysts said was partly aimed at highlighting Pyongyang's demands to the United States amid efforts to restart six-nation nuclear disarmament talks.

Crowley and Morrell both declined to comment on North Korea's motivations or any effect on US diplomatic efforts.

"It's always difficult to interpret the intentions behind North Korea's actions," Morrell said.

"We, however, have made it very clear that there is a path open to the North Koreans in the framework of the six-party talks to achieve the security and international respect that ...at least they say they seek," Morrell said.

"So provocative actions such as those that we saw yesterday are clearly not part of that path," he said.

North Korea last year tested a nuclear bomb for the second time and stormed out of the six-nation deal on ending its nuclear drive, although it later agreed to re-enter the negotiations.

But North Korea has since demanded that the United States first negotiate with it to draft a formal peace treaty to end the 1950-1953 Korean War, which ended in an armistice.