South Korea says Pyongyang fired two short-range missiles into sea on Monday, after four missiles were fired on Thursday

North Korea has fired two short-range missiles into the sea – the second such launch in less than a week – while annual military exercises between Seoul and Washington continue, South Korean officials said.

The launches appear to be a continuation of North Korea's protest against the drills it calls a preparation for an attack, and a test of its own weapons systems. They followed South Korea's announcement that Pyongyang fired four short-range Scud missiles with a range of more than 125 miles (200km) into North Korea's eastern waters last Thursday.

North Korea routinely test-fires short-range missiles, Analysts did not expect the launches to raise tensions, as was the case last spring when North Korea repeatedly threatened to provoke a nuclear war following its third nuclear test in February 2013. Recently, North Korea has pushed for improved ties with South Korea and made conciliatory gestures, including permitting rare reunions of Korean war-divided families last month.

On Monday, two projectiles fired from North Korea's east coast flew about 310 miles (500km) before landing in the high seas, South Korean defence ministry spokesman Kim Min-seok told reporters.

South Korea is trying to confirm what Pyongyang fired on Monday based on the speed and trajectory of the projectiles, but an initial investigation showed they were missiles, suspected to be Scud-series, a defence ministry official said, speaking on condition of anonymity in line with department rules.

He said the North Korean missiles flew past a South Korean air defence identification zone and landed in the waters below the Japanese defence zone.

Kim said the launches were made without prior notice. He described them as a provocation posing a serious threat to international aviation and maritime navigations and civilian safety. "North Korea is doing an act of double standard by taking a peace offensive ostensibly, but later launching reckless provocative acts," he said.

Chang Yong Seok of the Institute for Peace and Unification Studies at Seoul National University said the launches appeared to be part of North Korean military training aimed at coping with the South Korea-US drills. He said tensions could be heightened if North Korea tested a longer-range missile capable of hitting Japan or the US territory of Guam.

Analysts say North Korea's recent charm offensive toward South Korea is largely aimed at helping lure foreign investment and aid to help revive the country's troubled economy.

The two Koreas are divided along the world's most heavily fortified border since the 1950-53 Korean war ended with an armistice, not a peace treaty. About 28,500 American troops are deployed in South Korea to deter potential aggression from the North. South Korea and the US have said they have no intention of invading North Korea and that their ongoing springtime drills are defensive in nature.