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Hillary Clinton hugs Indonesian foreign minister Marty Natalegawa as they pose for a group photo along with other foreign ministers prior to the opening of the Asean Regional Forum yesterday. Image Credit: AP

Hanoi: US Secretary of State Hillary Clinton urged Asia on Friday to enforce tough sanctions against North Korea, which hit back by threatening a ‘physical response' to Washington's plans for joint military drills with South Korea.

Clinton, speaking in Hanoi at the Asia-Pacific's biggest security dialogue, also called on Myanmar's neighbours to pressure the country's military rulers for democratic reforms, and said Asia must join the global community in sending a ‘clear signal' to Iran to curb its nuclear ambitions.

"One measure of the strength of a community of nations is how it responds to threats to its members, neighbours and region," Clinton told the 27-member Asean Regional Forum, which includes regional powers China, Japan and Russia along with the United States, European Union and Canada.

Clinton on Wednesday unveiled new US sanctions against North Korea, blamed by both Washington and Seoul for the March sinking of a South Korean warship which killed 46 sailors and sharpened tensions over Pyongyang's nuclear programme.

The new US sanctions target North Korea's ruling elite and build on earlier United Nations sanctions which imposed broad curbs on dealings with the North in hopes of persuading it to abandon its atomic ambitions.

Clinton said it was essential Asian nations enforce the punitive measures to encourage North Korea "to take the steps it must" to stop nuclear development and seek real peace with South Korea.

A North Korean diplomat said the sanctions and plans for US and South Korean large-scale joint military drills would be met with a ‘physical response'.

"There will be physical response to the steps imposed by the United States militarily," Ri Tong-il, a member of Pyongyang's delegation at the security forum, told reporters. The military drills, he said, violated North Korean sovereignty.

Japan waded into the crisis, announcing plans to send four Maritime Self Defence Forces officers to the US-South Korea exercises off the west coast of the divided Korean peninsula as observers, responding to invitations from the two countries.

This will be the first time Japan's self defence forces join a joint exercise by the United States and South Korea starting this weekend, a Defence Ministry spokeswoman said. The four officers will be aboard US aircraft carrier George Washington.

Clinton also urged Asia-Pacific ministers to put more pressure on Myanmar — a member of the Association of South East Asian Nations (Asean) which anchors the forum — to enact real democratic reforms and allow elections later this year which will be both free and credible.

President Barack Obama's administration has expressed frustration that, despite US offers of greater engagement, Myanmar's military rulers have refused to budge on key demands. These include the release of an estimated 2,000 political prisoners, such as Nobel Peace laureate Aung San Suu Kyi.

It has also said it is concerned by reports that Myanmar, formerly known as Burma, is seeking North Korean help to develop its own nuclear programme, which, if true, could open an alarming new front in the battle against global proliferation.