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SEOUL, South Korea — North Korea fired three ballistic missiles off its east coast Monday, South Korea's military said, in a show of force timed to the G-20 economic summit in China.

North Korea regularly engages in missile and rocket tests, especially when international attention is turned to Northeast Asia. World leaders are gathering for the G-20 summit of advanced and emerging economies in the city of Hangzhou in eastern China.

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Beijing is the North's only major ally, but ties between the neighbors have frayed amid a string of nuclear and missile tests and what many outsiders see as other provocations in recent years.

A passenger watches a TV screen in Seoul broadcasting a report on North Korea firing ballistic missiles on Monday. KIM HONG-JI / Reuters

South Korea's Joint Chiefs of Staff said in a statement that the three missiles, launched from the western North Korean town of Hwangju, flew across the country before splashing in the waters off its east coast. Officials did not describe the range of the missiles.

Before the firing, on the sidelines of the G-20 summit Monday, South Korean President Park Geun-hye criticized the North for what she called provocations that are hurting Seoul-Beijing ties.

The launch comes four days before the 68th anniversary of the founding of North Korea's government, and days after South Korean and U.S. troops ended annual joint summertime military drills — which North Korea regularly describes as a dress rehearsal for invasion.

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Last month, worries about the North's weapons programs deepened after a missile from a North Korean submarine flew about 500 kilometers (310 miles), the longest distance achieved by the North for such a weapon.

The U.N. Security Council in late August strongly condemned four North Korean ballistic missile launches in July and August. It called them "grave violations" of a ban on all ballistic missile activity.