A North Korean soldier looks out at a worker along the riverfront of Sinuiju town across from the Chinese border town of Dandong. (Ng Han Guan/Associated Press)

North Korea fired a missile on Friday as it warned sanctions imposed by the United Nations Security Council in the wake of its recent nuclear test could result in defensive action.

"If the UN Security Council makes a further provocations, it will be inevitable for us to take further self-defence measures," North Korea's Foreign Ministry said in a statement Friday.

"There is a limit to our patience," the statement said.

The Security Council is considering imposing new sanctions against North Korea after it carried out an underground nuclear test on Monday and then fired several missiles off its coast.

South Korean navy sailors patrol near Yeonpyong Island, west of mainland South Korea, on Friday. (Yonhap, Ahn Jung-won/Associated Press)

The North again fired a missile from its Musudan-ni launch site on the east coast on Friday, said a South Korean government official, who spoke on condition of anonymity, citing the sensitivity of the matter.

It is the sixth short-range missile North Korea has test-fired since Monday's nuclear test.

South Korea's state news agency, Yonhap, said the missile test was a new type of ground-to-air missile with an estimated range of up to 260 kilometres.

As a sovereign state, the North has the right to conduct missile and nuclear tests, the statement said.

The statement called the Security Council "hypocrites."

The North's statement did not specify what sort of defensive response would be taken or what would be considered a provocation.

The country has previously warned the government no longer considers itself bound by the armistice that ended the Korean War.

It has also said it would respond with military force against any attempt to stop and search North Korean ships under the Proliferation Security Initiative, adding that such action would be considered an act of war.

Chinese fishing boats leave area

Tensions continued to rise on Friday, as China pulled fishing boats away from the coast to avoid any possible skirmishes between North and South Korea.

But U.S. Secretary of Defence Robert Gates said the situation is not a crisis and no additional U.S. troops will be sent to the region.

South Korean and U.S. troops facing North Korea raised their surveillance on Thursday to its highest level since 2006, when North Korea tested its first nuclear device. About 28,000 American troops are stationed across the South.

North Korea, whose 1.2-million-strong military is one of the world's largest, says it is merely preparing to defend itself against what it says are plans by the United States to launch a pre-emptive strike to overthrow its Communist government.

The United States has repeatedly denied any intention to attack North Korea.

Draft UN proposal expected next week

North Korea has been under UN sanctions that bar it from nuclear and ballistic activity since its first atomic test in 2006. But Pyongyang had threatened for weeks to carry out its second reported nuclear test after the UN Security Council condemned the April 5 launch of a long-range rocket.

The North claimed the test launch was part of its development of its space program, but other nations alleged it was a test of long-range missile technology.

The Security Council condemned Monday's nuclear test as a "clear violation" of a 2006 resolution barring the country from developing its nuclear program.

But putting together a new resolution to address the situation will take time because the issue is complicated, officials have said. But there are reports that there is wide agreement among world powers about what elements will be included in the sanction.

A list of proposals was sent Wednesday to the five permanent veto-wielding council members — the United States, Russia, China, Britain and France — and the two countries most closely affected by the nuclear test, Japan and South Korea.

A draft proposal is expected to be circulated next week.

With files from The Associated Press