A U.S. court has sentenced two Somali pirates to life in prison for hijacking a yacht in February, leading to the murders of four Americans.

Muhidin Salad Omar and Mahdi Jama Mohamed both pled guilty to piracy charges in May, but denied shooting anyone.

U.S. Attorney Neil MacBride called Somali piracy a scourge that is growing and becoming more violent. He said the life sentences handed down Monday send a strong message that anyone carrying out piracy against U.S. interests faces severe consequences.

Omar and Mohamed were among a group of Somali pirates and one Yemeni who hijacked the yacht, Quest, in the waters off East Africa in February. Four Americans on board were held hostage for several days before being shot dead.