North Korea fired seven ballistic missiles on Saturday, South Korea's defense ministry said, in an act of defiance toward the United States that further stoked regional tensions already high due to its nuclear test in May.

South Korea's Yonhap news agency said the missiles test-fired were 'Scud-type,' marking an escalation of recent saber-rattling by the reclusive North, which has fired several non-ballistic, short-range missile since the May 25 nuclear test.

North Korea is barred by United Nations resolutions from firing ballistic missile such as the Scud. A South Korean Defense Ministry official said more launches could come soon.

It was the biggest barrage of ballistic missiles the North has fired since it launched seven missiles in 2006 around the US July 4 Independence Day holiday, including its longest-range Taepodong-2.

The launches came as the United States has cracked down on firms suspected of helping the North in its trade in arms and missiles, which were subject to U.N. sanctions imposed after the nuclear test and are a vital source of foreign currency for the cash-short state.

An anonymous South Korean official quoted by Yonhap said the launch may have been intended to send a message to Washington, the North's main foe who for years has been trying to press Pyongyang to end its atomic ambitions and rein in missiles that threaten US allies South Korea and Japan.

'Today's missiles seem to have political purposes in that they were fired a day ahead of the U.S. Independence Day,' the agency quoted the official as saying.

Peter Beck, an expert on Korean affairs at the American University in Washington, said: 'If the North Koreans are trying to get out attention, it is difficult to see what they are actually trying to accomplish.'

South Korea's Defence ministry confirmed the North fired seven missiles off its east coast from morning to late afternoon that flew about 400 km (250 miles) and splashed into the sea.

'It is a provocative act that clearly violates U.N. Security Council resolutions,' Yonhap quoted a statement from South Korea's Foreign Ministry as saying.

Japan's foreign ministry said in a statement the country: 'strongly protests and regrets today's missile launches by North Korea as they are a serious act of provocation against the security of neighboring countries, including Japan.'

North Korea is thought to have more than 600 Scud-type missiles that include the Hwasong-5, with a range of about 300 km (185 miles) and the Hwasong-6, with a range of about 500 km (310 miles).

It also has more than 300 mid-range Rodong missiles that can hit all of South Korea and most of Japan. Weapons experts said the North does not have the ability to miniaturize a nuclear weapon to mount as a warhead on a missile.-Reuters