Four suspected people-smugglers were killed in an exchange of gunfire with the Libyan coastguard off western Libya on Thursday.

A German journalist travelling on the coastguard boat was wounded in the clash, which he said started when the coastguards tried to apprehend heavily armed gunmen stationed near an asylum-seeker boat, coastguard spokesman Ayoub Qassem said.

"The coastguard boat detected the gunmen's boat by radar during a patrol," Qassem told Reuters news agency.

"The gunmen were asked to stop but they refused to follow the rules, which means most likely they were smugglers of illegal migrants. They opened fire at the patrol. The coastguards fired back too."

Libya halts hundreds of Europe-bound refugees

Two of the suspected smugglers were arrested and one was missing, Qassem said. A Spanish cameraman and a Libyan fixer were also travelling on the coastguard boat, and both were unharmed, he said.

Libya's western coast is the departure point for the vast majority of refugees trying to reach Europe by sea, and powerful smuggling networks have long operated with impunity in the area.

They pack asylum seekers into flimsy inflatable boats usually carrying barely enough fuel to reach international waters, where most are picked up by European rescue craft or other vessels.

Libya's coastguard, parts of which are now receiving European Union training, occasionally intercepts boats and returns them to Libya. Some boats sink or run out of fuel.

By the end of last month, 23,125 asylum seekers had crossed the central Mediterranean to Italy and 595 were known to have died, an increase compared with the same period last year, according to the International Organization for Migration.