MADRID (AP) — More than 120 migrants were rescued Tuesday from the Mediterranean Sea while 13 more —including pregnant women and children— died in a crammed rubber raft, according to a Spanish rescue group.

Spain's Proactiva Open Arms said it rescued 121 men, 40 women and six children from the raft as it floated 15 miles (24 kilometers) north of the Libyan coastal town of Sabratha.

The 13 people whose bodies were found in the packed boat are thought to have died of asphyxiation, Proactiva spokeswoman Laura Lanuza said. They included the mother of four of the children who survived, she said.

Separately, a boat for nonprofit Save the Children came to the aid of some 90 migrants aboard a small boat off Libya, Italian news agency ANSA reported.

Both rescue operations were coordinated by the Italian coast guard.

Images taken by a news photographer traveling with the Proactiva aid group showed semi-naked bodies piled on the bottom of the raft amid scattered life vests.

It wasn't immediately clear what caused the deaths, but Lanuza said the perilous trip to European shores often proves fatal due to a combination of heat, a lack of water and oxygen deprivation in overcrowded boats.

Nearly 84,000 migrants arrived in Italy by sea during the first half of this year, a 20 percent increase from the same period last year, according to the International Organization for Migration. More than 2,200 others have died trying to reach Europe across the Mediterranean Sea.

The European Council on Tuesday extended the mandate of its naval operation targeting migrant smuggling until the end of 2018. It also expanded the operation to include monitoring illegal oil trafficking from Libya.

The EU launched Operation Sophia two years ago to disrupt smuggling networks, engage in sea rescues, and stem the flow of desperate migrants attempting the risky crossing from Libya to Italy in unseaworthy boats.

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AP reporter Frances D'Emilio in Rome contributed to this story.