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SEOUL, July 4 (Reuters) - North Korea test-fired two Scud-type missiles on Saturday, South Korea's Yonhap news agency said citing a government official, further stoking regional tensions after the North's nuclear tests and threats to boost its nuclear arsenal in response to U.N. sanctions.

"North Korea fired two missiles, which appear to be a Scud type, at around 8 a.m. today," Yonhap quoted the anonymous South Korean official as saying. "The missiles are estimated to have the range of about 500 km (310 miles)."

The North, which has a history of firing missiles at times of diplomatic friction, was hit with United Nations sanctions following its May 25 nuclear test. Saturday's launch also coincided with the United States' July 4 national holiday.

North Korea fired a rocket in April in what was widely viewed as a long-range missile test.

It then fired a barrage of short-range missiles after its May 25 nuclear test and fired off another salvo of similar missiles in early July.

The U.N. Security Council punished North Korea for the April long-range rocket launch by tightening existing sanctions.

North Korea said it had the right to fire the rocket in April as part of its civilian space programme and had threatened an intercontinental ballistic missile launch unless the Security Council apologised for the punishment.

In response to the nuclear test, the U.N. Security Council in June approved a resolution to ban the trade of weapons by North Korea including missile systems, which are a vital source of foreign currency for the cash-short state.

It also authorised U.N. member states to inspect North Korean sea, air and land cargo, requiring them to seize and destroy shipped goods that violate the sanctions. (Writing by Jon Herskovitz; Editing by Alex Richardson)

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