"North Korea fired an unidentified projectile in Sinpo, South Hamgyong Province, into the East Sea", South Korea's Joint Chiefs of Staff said, according to Yonhap news agency, using the local name for the sea between the Korean Peninsula and Japan.
Trump and Xi will hold their first face-to-face meeting on Thursday at the U.S. president's Mar-a-Lago resort in Florida where the growing tensions on the Korean peninsula are expected to be high on the agenda.
Pyongyang is banned from testing any ballistic missile technology under United Nations resolutions. The only thing that could worry the USA experts is the capability of North Korea's nuclear-tipped missiles to reach the US mainland.
The greatest threat would come from an intercontinental ballistic missile capable of reaching the United States, and Hyten testified the North Koreans are closing in on one.
Seoul called a National Security Council meeting and vowed to respond strongly in case of further provocations.
Despite angry opposition from Beijing, the USA last month started to deploy the first elements of THAAD in South Korea.
Seoul and Washington have maintained that Thaad will only be used to defend South Korea against Pyongyang's missile launches.
North Korea's nuclear program was expected to be an important talking point between Xi and Trump.
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Johnson said Britain called on Russian Federation to do everything possible to bring about a "political settlement in Syria". Elsewhere in Syria, at least seven people were killed in air strikes in Eastern Ghouta, near the capital Damascus.
South Korea and the USA have said the sole objective of the advanced system is to defend against missile launches from North Korea.
In early March, North Korea launched five medium-range Scud-type missiles.
North Korea's foreign ministry on Monday criticised the USA for its tough talk and for an ongoing joint military exercise with South Korea and Japan which the North sees as a dress rehearsal for invasion.
US Secretary of State Rex Tillerson confirmed Pyongyang had launched "yet another" ballistic missile.
Photos taken by the club's patrons and later posted on Facebook captured Japanese and USA officials responding in real-time to the incident, sparking criticism about why such important meetings were not conducted in a more secure location.
Four North Korean missile bases that pose a threat to South Korea lie within 300 km from central South Korea, six within 400 km, and nine within 550 km.
In brief comments televised nationally, Abe also said Trump had told him all options were on the table.
The US recently said it would take possible unilateral action against Pyongyang if China, the North's main ally, failed to help pressure Pyongyang into abandoning its nuclear and possibly missile programs. North Korea sees the drills as an invasion rehearsal.