WASHINGTON, USA - The White House said Thursday that North Korea's latest missile launches were the latest in a string of 'provocative' acts.

But the White House also said that broadly-backed international sanctions imposed on North Korea were starting to take effect and raised hopes that Pyongyang will yield to the pressure.

'The North Koreans said they were going to launch these missiles. I don't think that's surprising that they've launched these missiles,' White House spokesman Robert Gibbs said.

'I take the North Koreans at their word that they're going to continue their provocative actions,' he added.

But Gibbs said North Korea was beginning to feel the effect of UN Security Council sanctions imposed after North Korea staged a nuclear weapons test - its second - on May 25.

The sanctions call for beefed-up inspections of air, sea and land shipments going to and from North Korea, and an expanded arms embargo.

'It is clear sanctions are having an impact,' Gibbs said, citing cooperation from Russia and China, countries that had previously resisted sanctions against North Korea.

'First and foremost, the administration is working to ensure the vigorous implementation of those sanctions,' Gibbs added.

He also suggested that North Korea was beginning to respond to the pressure, but did not elaborate.

'I think the impact alone of a united international community is tremendously important. Obviously, there have been positive developments over the past few days as it relates to the actions of the North Koreans,' he said.

When asked if he was suggesting that North Korea showed no signs it was preparing to launch another long-range missile, Gibbs replied: 'I don't want to get into intelligence matters.'

Washington has said it is not ruling out the possibility of a long-range missile launch toward Hawaii on or around July 4, the US Independence Day, although the Pentagon has expressed doubts about such a scenario.

State Department spokesman Ian Kelly echoed many of the points by Gibbs.

'We've seen reports that they've launched, I think, four missiles. And these kinds of reports are not new. These kinds of actions, of course, are not helpful, (they) are dangerous,' Kelly said.

'The international community has spoken loudly. And North Korea, as I say, knows exactly what it has to do. It has to cut out these kinds of provocative actions and return to denuclearization talks,' he said.

After it was condemned at the United Nations for launching a long-range missile on April 5, North Korea bolted six-nation talks aimed at scrapping its weapons-grade nuclear programs.

The talks involve the United States, South Korea, Japan, China and Russia.