By Jack Kim

SEOUL (Reuters) -North Korea fired short-range ballistic missiles into the sea on Monday for the first time in two months, as U.S. Secretary of State Antony Blinken visited Seoul for a conference hosted by President Yoon Suk Yeol on advancing democracy.

South Korea's military said several short-range missiles flew about 300 km (186 miles) after being fired between 7:44 a.m. and 8:22 a.m (2244 to 2322 GMT Monday) from Pyongyang, the North's capital, landing off the east coast.

It condemned the launches as a "clear provocation" and said it was sharing information on them with the United States and Japan.

Japan's defence ministry said three missiles were launched and travelled about 350 km, with a maximum altitude of 50 km.

Japanese Prime Minister Fumio Kishida condemned the launches after his country's coast guard also reported the firing of what it said appeared to be a ballistic missile and specified that it had already ended its flight.

Japan later said that it had detected what appeared to be a second ballistic missile launch by the North, and that both fell outside its exclusive economic zone area.

"North Korea's series of actions threaten the peace and security of our region and the international community, and are absolutely unacceptable," Kishida said, calling the launch a violation of U.N. resolutions.

North Korea's military has been conducting exercises using conventional weapons in recent weeks, often personally overseen by the isolated state's leader, Kim Jong Un.

The show of force by Pyongyang comes just after the militaries of South Korea and the United States finished 10 days of large-scale annual joint military drills last Thursday.

On Sunday, the South Korean military also mobilised marines, attack helicopters and amphibious assault vehicles in drills aimed at surging troop numbers to reinforce western islands near the sea border with North Korea. The North shelled the islands in 2010.

Blinken is among senior officials from around the world attending the Summit for Democracy conference, which opens on Monday. He will also meet his South Korean counterpart, foreign minister Cho Tae-yul.

The summit is an initiative of U.S. President Joe Biden aimed at discussing ways to stop democratic backsliding and erosion of rights and freedoms worldwide.

In its last ballistic launch on Jan. 14, North Korea fired what it said was an intermediate range hypersonic missile using solid fuel on to test new booster engines and a manoeuvrable warhead.

A month later, it launched multiple cruise missiles off its east coast, including what it said was a new anti-ship missile.