All four hostages, which included a Fuller Theological Seminary graduate, aboard a yacht were shot dead early Tuesday after they were held captive by Somali pirates.

The U.S. Central Command said negotiations for the release of the hostages were ongoing when there was gunfire at approximately 1 a.m. ET Tuesday.

U.S. Forces responded to the gunfire aboard the pirated vessel, named the Quest, by boarding the yacht but discovered that all the hostages had been shot.

"Despite immediate steps to provide life-saving care, all four hostages ultimately died of their wounds," the U.S. Central Command said in a statement.

The Quest was owned by Scott Adams, who obtained a master of theology degree from Fuller in 2010, and his wife, Jean. Two other Americans – Phyllis Mackay and Robert A. Riggle – were on board when the vessel was hijacked by pirates off the coast of Oman on Friday.

U.S. Forces responded with four U.S. Navy warships as they sought to recover the Quest. They were closely monitoring the Quest for three days before the hostages were shot.

Gen James N. Mattis, U.S. Central Command Commander, stated, "We express our deepest condolences for the innocent lives callously lost aboard the Quest."

Fuller Seminary had requested urgent prayers for the four hostages on Monday.

“Adam … is a beloved friend of the seminary. We ask that all members and friends of the Fuller community keep Scott, his wife, and their two accompanying friends in their thoughts and prayers,” the Southern California-based seminary stated on its website.

Scott and Jean Adams were retired and had been sailing around the world for the past six years on their yacht. The couple was on a worldwide trip to distribute Bibles.

On the couple's website, Jean Adams wrote, “Another aspect of our travels is friendship evangelism – that is, finding homes for thousands of Bibles, which have been donated through grants and gifts, as we travel from place to place.”

The couple wrote on their website their 2011 trip plans, which began in Phuket, an island off of Thailand, and would end in Crete in April. In between, the couple would stop in Sri Lanka, India, Oman, and Djibouti, among other places.

After Crete, the couple had planned to also travel to Turkey and London.

According to the U.S. Central Command, it is believed that 19 pirates were involved in the hijacking of the Quest. Two pirates were killed during confrontation on the vessel and 13 were captured and detained. Two were already in U.S. Forces custody and another two were found dead aboard the yacht.

Christian Post reporter Michelle A. Vu contributed to this story.