By Louis Charbonneau and Jack Kim
UNITED NATIONS/SEOUL, March 8 (Reuters) - The United Nations imposed new sanctions on North Korea aimed at curtailing its nuclear and ballistic missile programmes and China, the isolated regime's only major ally, said it wanted the measures fully implemented.
The sanctions were approved just hours after North Korea threatened the United States with a pre-emptive nuclear strike, a largely empty warning since experts believe Pyongyang does not have the capability to hit the U.S. mainland.
With tensions high on the Korean peninsula, North Korean leader Kim Jong-un visited military units on the frontline of any potential clash with South Korea and the United States, which has 26,000 troops stationed in the South.
The new U.N. Security Council measures announced on Thursday tighten financial restrictions on North Korea and crack down on its attempts to ship and receive banned cargo.
They were agreed after three weeks of negotiations between the United States and China, which has a history of resisting tough penalties against its impoverished neighbour.
"When North Korea tries to move money to pay for its nuclear and ballistic missile programmes, countries must now block those transfers even if the money is being carried in suitcases full of bulk cash," said the U.S. ambassador to the United Nations, Susan Rice.
China's U.N. ambassador, Li Baodong, said Beijing wanted "full implementation" of the new resolution.
The success of the new measures, council diplomats said, would depend to a large extent on the willingness of China to enforce them more strictly than it has in the past.
If carried out to the letter that would see China inspecting shipments from major ports such as Dalian, which could be a big blow to Kim, who appears to have risked distancing himself from his sole major ally and trading partner.
In a statement released late on Thursday, China's Foreign Ministry called the sanctions a "necessary and moderate response" to North Korea's Feb. 12 nuclear test.
The U.N. resolution also specifies some luxury items North Korea's elite is not allowed to import but its main aims are to stop financial institutions dealing with North Korea and to staunch the flow of cash flowing into the country into what defectors have dubbed the "royal court" fund, used to finance the Kim family's opulent lifestyle and its nuclear ambitions.
"These sanctions will bite and bite hard," said Rice.
The sanctions were designed to make the punitive measures more like those used against Iran, which Western officials say have been surprisingly successful.
George Lopez, a professor at the University of Notre Dame in Indiana and a former member of the U.N. panel that monitors North Korea sanctions compliance, said the new measures should have a real impact on North Korea's movement of money and constrain access to equipment for its nuclear and missile programmes.
"Now, we may yet see another launch or a bomb test, but over the medium term this resolution will degrade DPRK capabilities to grow its programme," Lopez said, using the acronym for the Democratic People's Republic of Korea.
THREATS AND WAR GAMES
Washington said North Korea's nuclear threats would only lead to Pyongyang's further international isolation and declared the United States was "fully capable" of defending itself.
President Barack Obama's administration also said it had reassured South Korea and Japan "at the highest levels" of its commitment to deterrence, through the U.S. nuclear umbrella and missile defense, in the face of the new threats.
North Korea has accused the United States of using military drills in South Korea as a launch pad for a nuclear war and has again scrapped the armistice with Washington that ended hostilities in the 1950-53 Korean War.
Its soaring anti-American rhetoric is seen by experts as a ploy to be taken as a serious threat and to force Washington back to the negotiating table.
"This might have been a workable strategy in the past, but there will be little appetite to negotiate until North Korea shows it is committed to real change," said Matt Stumpf, Washington director of the Asia Society.
A more likely option for Pyongyang than a full-scale conflict is to stage a series of clashes along a disputed frontier with the South, a sea border known as the Northern Limit Line, which has been the scene of previous clashes.
In 2010, the North was widely believed to have sunk a South Korean naval vessel killing 46 sailors, something Pyongyang has denied. In the same year it shelled a South Korean island in the disputed area, killing civilians.
Kim Jong-un visited two military units on islands near the line on Thursday, according to state news agency KCNA, on what it termed "the biggest hotspot" in the waters of the Korean peninsula and where he urged the units to "make the first gunfire" in response to any attack on its territory.
North Korea was conducting a series of military drills and getting ready for state-wide war practice of an unusual scale, South Korea's defense ministry said earlier. (Additional reporting by Michelle Nichols at the United Nations, Paul Eckert and Anna Yukhananov in Washington and David Chance in Seoul; Editing by Christopher Wilson and Dean Yates)