Spain's maritime rescue service says it picked up 162 migrants who were attempting to make the perilous trip across the Mediterranean Sea to Europe this weekend.

The service said its rescue craft intercepted 121 people traveling in three separate boats on Saturday and pulled another 41 passengers from a fourth boat on Sunday.

Each year, tens of thousands of migrants attempt to reach Spain and other southern European countries by crossing the Mediterranean in smugglers' boats. Most of the vessels are unfit for open water, and thousands of people drown each year.

The United Nations says 615 migrants have died crossing the Mediterranean so far this year. A total of 22,439 travelers reached European shores, 4,409 of them arriving in Spain, during the first four months of 2018.