Image copyright EPA Image caption South Korea's Defence Minister Jeong Kyeong-doo also apologised to citizens last month

South Korea has apologised again for allowing a North Korean fishing boat to reach the nation's shore in a major breach of its borders.

The incident, in June, saw the small vessel carrying four fishermen slip through South Korean waters and dock at a port.

The government called the incursion a "grave mistake", but rejected claims it had covered up the incident.

Peninsula tensions remain despite recent landmark meetings with the US.

According to Korean media, the boat was allowed to drift, undetected, through South Korean waters for 57 hours before it landed at the eastern port of Samcheok.

Authorities were only alerted after the fishermen asked local South Korean villagers for a mobile phone to contact relatives.

Two of the four fishermen have since defected to the South, while the others have asked to be returned to the North.

Security breach

On Wednesday, South Korea's defence ministry said a weeks-long investigation into the case had found failures in the military's surveillance.

Authorities had also erred in informing the public properly about the situation, Defence Minister Jeong Kyeong-doo said.

"We failed to make full and precise explanations to the public, as we made a wrongful judgment about the early situations," said Mr Jeong according to the Yonhap news agency.

The address comes just a few days after a historic meeting between Korean leaders and US President Donald Trump at the Demilitarized Zone (DMZ), an area that divides the two Koreas.

Media playback is unsupported on your device Media caption Mr Trump became the first sitting US president to set foot in North Korea on Sunday

The surprise visit by Mr Trump was hailed by North Korean media as an "amazing event".

However, critics dismissed the occasion as an act of political theatre which did not make substantial progress towards North Korea giving up its nuclear weapons.