SEOUL, June 5 (Reuters) - North Korea fired at least one ballistic missile towards the sea off its east coast on Sunday (Jun 5), a day after South Korea and the United States wrapped up their first combined military exercises involving an American aircraft carrier in more than four years.

South Korea's Joint Chiefs of Staff said that North Korea had fired an "unknown" missile, without elaborating.

Japan's government also reported that the North had launched a suspected ballistic missile.

The launch also followed a visit to Seoul by the United States point man on North Korean affairs, US special representative Sung Kim, who departed on Saturday.

He met his South Korean and Japanese counterparts, Kim Gunn and Funakoshi Takehiro, on Friday to prepare for “all contingencies” amid signs that North Korea was preparing to conduct a nuclear test for the first time since 2017.

Washington has made very clear directly to Pyongyang that it is open to diplomacy, Kim said during the visit, which wrapped up on Sunday, noting that he was willing to discuss items of interest to Pyongyang, such as sanctions relief.

Last week, the United States called for more United Nations sanctions on North Korea over its ballistic missile launches, but China and Russia vetoed the suggestion, publicly splitting the UN Security Council on North Korea for the first time since it started punishing it in 2006, when North Korea conducted its first nuclear test.

In recent weeks, North Korea has test-fired a range of missiles, including its largest intercontinental ballistic missile (ICBM).

North Korea's last tests were on May 25, when it launched three missiles after US President Joe Biden ended an Asia trip where he agreed to new measures to deter the nuclear-armed state.

The first missile appeared to be the North's largest ICBM, the Hwasong-17, while a second unspecified missile appeared to have failed mid-flight, South Korean officials said at the time. The third missile was a short-range ballistic missile (SRBM).

On Saturday, South Korean and American ships concluded three days of drills in international waters off the Japanese island of Okinawa, including air defence, anti-ship, anti-submarine and maritime interdiction operations, South Korea's Joint Chiefs of Staff said.

The exercises included the USS Ronald Reagan, a 100,000-ton nuclear-powered aircraft carrier, among other major warships.

South Korean President Yoon Suk-yeol, who took office on May 10, had agreed with Biden to increase bilateral military drills to deter North Korea.

North Korea has criticised previous joint drills as an example of Washington's continued "hostile policies" towards Pyongyang, despite its talk of diplomacy.