Two tourists on holiday in Morocco were shot dead by Algeria's coastguard when they reportedly strayed across the maritime border between the two Mediterranean countries.
Bilal Kissi from Morocco, and Abdelali Merchouer, who holds dual French-Moroccan citizenship, came under fire after taking a wrong turn off the beach resort of Saidia on Morocco's north-east tip, local media reported.
A third member of the group was arrested by the coastguard, whose personnel patrol the closed border between the two states.
There were four men in the group on Tuesday, all riding jet skis.
Morocco launched a probe into the deaths on Friday.
The French Foreign Ministry reported the death of one citizen, without providing further details. It said another French national has been detained in "an incident involving several of our nationals".
"We got lost but we kept going until we found ourselves in Algeria," Mohamed Kissi, the brother of the man who died, told the Moroccan website Al Omk.
"We knew we were in Algeria because a black Algerian dinghy came towards us" and those on board "fired at us", he said.
"Thank God I wasn't hit, but they killed my brother and my friend. They arrested my other friend," he added.
"Five bullets hit my brother and my friend. My other friend was hit by a bullet," Mr Kissi said. "We got lost and we were out of fuel."
He said he was picked up by the Moroccan navy who took him back to the Saidia marina.
A fisherman posted video of a lifeless body floating in the sea, sparking anger in Morocco.
Tensions between Algeria and Morocco have increased recently over Morocco's Sahara region, which is claimed by an Algerian-backed separatist group.
The border between the North African countries has been closed since 1994, and Algiers severed ties with Rabat in 2021 after accusing its neighbour of "hostile acts", an accusation Morocco called "completely unjustified".
Algeria's President Abdelmadjid Tebboune said this year that relations with Morocco had reached “the point of no return”.
A Moroccan government spokesman declined to comment on the shooting, telling AFP it was "a matter for the judiciary".
There was no immediate comment from Algeria.