CONAKRY, Guinea (AP) — Guinea’s military confirmed the detention of 16 Sierra Leonean soldiers after accusing them of crossing the border and raising their flag on Guinean soil.

The two West African countries have been involved in a border dispute for more than two decades, stemming from the Sierra Leonean Civil War between 1991 and 2002. Sierra Leone’s government had invited Guinea to help defend its eastern borders during the war, but the Guinean troops didn’t completely withdraw after the war.

The GuineanMinistry of National Defense said in a statement, issued late Tuesday, the soldiers entered the district of Koudaya in Faranah, a border region in Guinea, without authorization, where they“set up a tent and raised their national flag”. Guinean authorities also seized their equipment and supplies.

The Sierra Leonean authorities earlier Tuesday said several members of a security unit, including an officer, had been apprehended while making bricks for a border post in Kalieyereh in the district of Falaba on Monday.

Last year, the Guinean military entered a mineral-rich border town in Sierra Leone, reigniting the tension.