ROME — The medical aid group Doctors Without Borders said Saturday that it was temporarily suspending the operations of its ship used to rescue migrants because of what it said were threats from Libya’s Coast Guard.

The crews of the Libyan vessels have become more aggressive in patrolling the coasts where human traffickers launch boats crowded with migrants desperate to reach Europe.

The aid group said the rescue coordination center operated by Italy’s Coast Guard had informed it on Friday that the Libyan threats posed a security risk. The group added that the Libyan authorities declared their own rescue area, extending into international waters, the same day.

Doctors Without Borders said that its medical crew would keep working from a ship operated by another aid group but that its own vessel, Prudence, would not be involved in rescues.