Hundreds of people staged separate protests in Seoul against the joint South Korea-United States military exercises known as Ulchi Freedom Guardian (UFG) which began on Monday.

Three groups held three different protests in the South Korean capital, with the first - which included some 100 people - being held in front of the statue of King Sejong near the US Embassy in downtown Seoul, an epa journalist reports.

Protesters held up large red and yellow signs with anti-war messages printed on them, such as "Stop the War" in Korean and "Trump - stop your gab" in English, in apparent reference to the recent tense verbal exchanges between US President Donald Trump and the North Korean government.

A second protest of about 10 people was held further north in front of the presidential Blue House, where marchers held up signs that read "Double Freeze. US-S.Koera: Stop! UFG. N.Korea: Stop! Nuclear/missile test."

The Blue House protesters were reportedly vastly outnumbered by some 150 police officers who surrounded them.

A third group - about 50 members of the People's Solidarity for Participatory Democracy (PSPD) - held a flashmob protest in front of Seoul City Hall.

They spread on the ground a large banner that read "Peace not war", and arranged themselves in a giant peace sign using colored umbrellas.

In a statement about Monday's action on the PSPD website, the organization said "In times of conflict, small misunderstandings and accidental actions can aggravate things" and denounced the "vicious cycle" of military exercises and North Korean criticism that risks further confrontation.

The large-scale annual UFG military drills involving some 50,000 South Korean soldiers and 17,500 US troops are due to be held from Monday until Aug. 31.

The exercises follow heated rhetoric and threats between Washington and Pyongyang, which harshly condemns the joint military exercises as preparations for invasion of the Stalinist state.