A Moroccan man has described how the Algerian coastguard opened fire on him and three other tourists who had strayed into Algerian waters.
Mohamed Kissi was the only survivor to make it back. His brother and a friend were killed and another friend is said to be in Algerian custody.
"They charged, then began to shoot behind us," Mr Kissi told French television network BFM.
Morocco has opened an investigation and there has been no comment from Algeria.
The two nations have a long history of tension, tied to Morocco's claims to the disputed territory of Western Sahara.
The border between them was closed in 1994, with Algiers severing diplomatic ties two years ago. It accused Morocco of hostile acts - an allegation rejected by Rabat.
The party of four on two jet skis had set off from the Moroccan resort of Saidia on Tuesday when they were shot.
Mr Kissi described how they had got lost as night fell and realised they had strayed into Algerian territory when they saw boats of the Algerian coastguard approach.
"They charged into us," he said. His brother, Bilal, signalled for them to turn back.
"They started shooting behind us," Mr Kissi said.
The shooting sparked anger in Morocco after a fisherman posted footage of a lifeless body floating in the sea. It was that of Bilal Kissi, who lived in France. He was buried on Thursday.
Abdelali Mechouar has been named as the second man killed. His body is still in Algeria, according to Moroccan news site Le360.
Smail Snabe - who also has French nationality - reportedly appeared before a prosecutor in Algeria on Wednesday but no details were given.
Algeria and Morocco share a border nearly 2,000km (1,242 miles) long which has been a source of tension since independence from French colonial rule.
It was closed in 1994 for security reasons after Islamist militants attacked a hotel in the historic Moroccan city of Marrakesh.
Morocco-Algeria dispute: The basics
What is the dispute about? The two countries have border disputes which date back to the era of French colonisation - and even fought a war in 1963.
And since then? Relations have never recovered. Algeria backs the Polisario Front, which is fighting for Western Sahara's independence from Morocco.
What are the effects? The long border through the Sahara Desert remains tightly closed - there is no direct legal trade between the two neighbours.