Throughout last week, South Korean officials had warned the North could launch another intercontinental ballistic missile in defiance of UN sanctions and amid an escalating standoff with the United States.
Mr Fallon said: "I'm very concerned at the situation in the Pacific, the U.S. is fully entitled to defend its own territory, to defend its bases and to look after its people".
The much stronger version proposed by the U.S. last week, included the first asset freeze directed at Kim Jong-un, a complete ban on oil sales to his regime, and a mandate for warships from any member state to inspect ships suspected of carrying contraband to or from North Korea, and to enforce inspect using "all necessary measures".
His business has already been harmed by worsening US-North Korea ties: a boat load of American tourists headed to the country had to be canceled after Washington banned its citizens from visiting North Korea.
"And today, the Security Council is saying that if the North Korean regime does not halt its nuclear program, we will act to stop it ourselves", the US Ambassador to the UN, Nikki Haley, said as the 15-membered UN body passed the resolution 2375 on North Korea.
But China and Russian Federation, which both hold veto power in Security Council, would only agree to the compromise version enacted, and both expressed their determination to see a return to dialogue to resolve the issue.
It also bans joint ventures with North Korean entities, except for non-commercial public utility infrastructure projects not generating profits, and calls for the inspection of vessels on the high seas, if there are reasonable grounds to believe the cargo of such vessels is prohibited items.
North Korean leader Kim Jong-un sparked global condemnation with his country's latest nuclear blast.
"The North Korean regime is still getting some fuel supplies from China, which can keep its most essential operations functioning", he said.
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A U.S. official, familiar with the council negotiations and speaking on condition of anonymity, said North Korea imports some 4.5 million barrels of refined petroleum products annually and four million barrels of crude oil.
Specifically, this resolution will result in a 30% decrease in total oil imports by cutting off over 55% of refined petroleum products going to North Korea, the USA official told CNN.
Asked if the Seoul government would draw up its own sanctions on the North in line with the UNSC's latest step, he said that it is important to make sure that all existing resolutions and sanctions are faithfully implemented.
While President Donald Trump's administration does not rule out military options in dealing with the threat posed by North Korea, a USA pre-emptive strike is an unlikely scenario in addressing the nuclear standoff, according to security experts.
The US and its allies argue that tougher sanctions will pile pressure on Kim's regime to come to the negotiation table to discuss an end to its nuclear and missile tests. But the US official said North Korea now receives about 4.5 million barrels of refined petroleum products, which would mean a more than 50 percent cut.
North Korea imports all the crude oil it consumes-some 520,000 tons a year-most of which comes from China.
Chinese UN ambassador Liu Jieyi again called for talks "sooner rather than later". The proposal says the Security Council is committed to restarting six-party talks aimed at negotiating a complete denuclearization of the Korean peninsula.
China's United Nations ambassador urged the council to adopt the freeze-for-freeze proposal and urged the U.S.to pledge not to seek regime change or North Korea's collapse.
"If China and others continue to help North Korea evade sanctions, they should not do business in the United States anymore".
Monday's vote is seen as a key test of resolve for the council, which united last month to adopt a resolution meant to reduce the impoverished country's export earnings by up to a billion dollars.