That is about 20km (12m) south-east of where the North conducted its sixth and most powerful nuclear test on September 3, an official from the Korea Meteorological Administration in Seoul said.
A CTBTO spokeswoman said Zerbo's remark about a "smaller magnitude" referred to its monitoring of an event in North Korea on September 3 which the agency described as consistent with a man-made explosion but stopped short of calling a nuclear blast, pending testing for airborne radioactivity.
"The quake is presumed to have occurred naturally", an agency official said, according to South Korea's Yonhap news agency.
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"Our analysis shows that it was a natural quake".
Earlier this week the foreign minister said his country could test a powerful nuclear weapon over the Pacific Ocean in response to Trump's threats of military action.
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"Chinese government authorities will issue a notice based on the export situation when approaching the upper limit, and from that date implement a prohibition on exports of refined oil products to North Korea for the year", it said. A South Korean expert said the quake could have been caused by geological stress created from the recent nuclear explosion.
Monitoring groups estimate that the nuclear test conducted in North Korea earlier this month had a yield of 250 kilotons, which is 16 times the size of the U.S. bomb that destroyed Hiroshima in 1945.
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North Korea's recent missile launches over Japan especially drew stern rebukes from Tokyo and the global community. All six of North Korea's nuclear tests thus far, dating to 2006, have been conducted in underground tunnels.
"The United States is still taking an attitude of skepticism toward North Korea's nuclear capabilities", Lewis said.
The Commerce Ministry said the exports of refined petroleum to Pyongyang will be limited to 2 million barrels per year and sales of liquefied natural gas banned outright, effective January 1, 2018.
In recent months, the North has launched a pair of still-developmental ICBMs it said were capable of striking the continental United States and a pair of intermediate-range missiles that soared over Japanese territory.
Saturday's detection comes at a time of rising tensions between the United States and North Korea, with North Korean dictator Kim Jong Un and President Donald Trump engaging in an escalating war of words.
Experts say this move could cut off a major source of foreign currency for Pyongyang, as textiles are one of country's major exports, estimated by IHS Markit analysts to value $750m. "They can can do business with the United States or North Korea, but not both". The Pentagon said the mission in global airspace showed how seriously President Donald Trump takes North Korea's "reckless behavior".
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Kurds make up the fourth-largest ethnic group in the Middle East and are spread among parts of Iraq, Syria, Iran and Turkey. Last Monday, the Turkish army launched a highly visible military drill near the Habur border crossing to Iraq.