The Algerian coastguard has shot dead two tourists holidaying in Morocco who reportedly strayed into Algerian waters on their jet skis.
They were among four French-Moroccan dual nationals who had set off from the Moroccan resort of Saidia.
A third member of the group was arrested by the coastguard which patrol the two states' closed border.
The two nations have a long history of tension, tied to Morocco's claims to the disputed Western Sahara.
The border between them was closed in 1994, with Algiers severing ties two years ago. It accused Morocco of hostile acts - an allegation rejected by Rabat.
The shooting sparked anger in Morocco after a fisherman posted footage of a lifeless body floating in the sea.
Mohamed Kissi was the only one of the group of four to make it back to Morocco, AFP news agency reports, quoting Moroccan media.
"We got lost but we kept going until we found ourselves in Algeria," said Mr Kissi, whose brother Bilal was killed. He said the group had also run out of fuel.
"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," he added.
Mr Kissi denied the group had tried to escape when they were discovered by the coastguard, telling local media that his brother had tried talking to officials before he was shot.
"They arrested my other friend. Five bullets hit my brother and my friend. My other friend was hit by a bullet."
Mr Kissi said he then tried to swim back to Saidia and was eventually picked up by the Moroccan navy.
His cousin, the actor Abdelkarim Kissi, has called on the Moroccan authorities to bring the case to international courts.
"They killed Bilal Kissi my little cousin," he wrote on social media.
"His only fault was crossing the Algerian territorial waters, he was on vacation with his friends."
Abdelali Merchouer has been named as the second man killed.
His body is still in Algeria, according to Moroccan news site Le360.
The man arrested by the Algerian coastguard, named as Smail Snabe, reportedly appeared before a prosecutor on Wednesday but no details were given.
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.
The two nations 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 bombed 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.