Doctors Without Borders is temporarily suspending the activity of its migrant rescue ship due to alleged threats from Libya's coast guard.

The humanitarian group said Saturday that the rescue coordination center operated by Italy's coast guard has informed it that the Libyan threats pose a security risk.

The group says Libyan authorities declared their own rescue area, extending into international waters, on Friday.

Doctors Without Borders says its medical crew will keep working from a ship operated by another aid group while its own vessel, Prudence, isn't operating.

Humanitarian groups have had ships monitoring the Mediterranean Sea outside of Libya's territorial waters to help rescue many of the hundreds of thousands of migrants trying to reach Europe on distressed smugglers' boats.