But for unexplained reasons the two sides did not use it when Chinese boats harassed an American surveillance ship, the Impeccable, in the South China Sea in March.
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The unrest might have petered out but for an unexplained escalation.
His death is being treated as unexplained but not suspicious.
Members of the Association of South-East Asian Nations (ASEAN), alarmed by China's vague, unexplained but sweeping claim to sovereignty over most of the South China Sea, encouraged America to involve itself in the issue.
But past violations and unexplained traces of (potentially militarily useful) highly enriched uranium suggest that Iran is using the cover of electricity generation to acquire nuclear-weapons capability.
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Police are treating his death as unexplained, but not suspicious.
But astronomical observations have revealed unexplained outflows of matter from the vicinity of black holes.
It said there had been an "objective and detailed" re-investigation but the death was still being treated as unexplained.
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Norfolk Police said there had been an "objective and detailed" re-investigation but the death was still being treated as unexplained.
The longtime head of the Pemex union, who had been expected by many to fight any changes but has been the subject of questions about unexplained family wealth, pledged his support.
The xenon might have originated in China or Russia, but the most likely place was the land of unexplained events, the Democratic People's Republic of Korea.
But the influence of cosmic rays could resolve other as yet unexplained cycles in tree growth found in studies in North America.
The death of his 48-year-old wife remains unexplained pending further tests, police said Friday, but the heiress's previous problems with drugs are well documented.
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Elias Muhanna, a professor at Brown University in the US and editor of the Qifa Nabki blog on Lebanese politics, said the allegations were a "strange, unexplained aspect" of Mr Hassan's past, but had not dented his standing in the Sunni community.
But experts also said they believe there is a real and unexplained increase going on, too.
They said unexplained fatigue was a common problem in doctors' surgeries, but it was as yet unknown whether iron supplements could help these women.
Some of the pay difference is related to college major women tend to pursue lower-paying degrees like education but the researchers found that one-third of the pay gap is unexplained.
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But it was ominously reminiscent of the apparently random and still mostly unexplained bombings that brought terror to Italy from the late 1960s to the early 1980s.
Ms Martin was taken through the injuries Millie had suffered before her death, but said that, apart from seeing her daughter hit her ear on a chair, her other bruises were "unexplained".
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