China will observe a UN resolution on North Korea and promises to honor it, foreign ministry spokeswoman Hua Chunying said on Wednesday at a daily press briefing.

"We will firmly follow the UN resolution and honor related international obligations," Hua said when asked whether China will follow the resolution, which imposes sanctions on North Korea.

"The UN resolution is clear. China is a permanent member of the United Nations Security Council and a responsible member of the international community," she said.

The remarks came amid increasing international concerns over nuclearization of the Korean Peninsula.

South Korea said on Wednesday it had agreed to buy a fleet of US Apache attack helicopters in a deal reported to be worth $1.5 billion, at a time of heightened tensions with the North, AFP reported.

The decision comes as the Peninsula remains in a state of heightened military tension with the North threatening "thermo-nuclear war," angered by fresh UN sanctions and joint South Korea-US military exercises in March.

After the purchase, South Korea will be the fourth country to buy the four-blade, twin-engine helicopter after the United States, Taiwan and Saudi Arabia, South Korea's Yonhap News Agency said.

North Korea also barred a delivery of supplies to South Koreans in the closed Kaesong industrial zone Wednesday, as the South said it was time to stop rewarding Pyongyang's provocations.

US President Barack Obama said on Tuesday he expects more posturing and provocation by the North and, while he does not believe the Asian nation has the capacity to mount a nuclear weapon on a ballistic missile, the US is preparing for "every contingency," said Reuters.

Obama said he believes the North's saber-rattling is similar to past patterns of behavior. However, the US is taking precautionary measures, he said.

"We have to make sure that we are dealing with every contingency out there," Obama said. "And that's why I've repositioned missile defense systems - to guard against any miscalculation on their part.

Agencies