LONDON -- A powerful 6.3-magnitude earthquake struck western Afghanistan early Sunday, the U.S. Geological Survey said.

The quake, which was centered about 30 km north-northwest of Herāt, followed a series of powerful tremors that have killed thousands.

"This earthquake was preceded by three other M 6.3 earthquakes in the previous days," USGS said in a statement. "One M6.3 occurred on October 11th and two others occurred about 30 minutes apart on October 7th."

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