GIOIA TAURO, Italy (AP) -- A United States cargo vessel loaded with hundreds of tons of Syria's chemical weapons has pulled out of an Italian port, as part of the final phase of the international effort to rid Syria of its chemical weapon stockpile.

The MV Cape Ray steamed out of the port of Gioia Tauro after a 12-hour operation to transfer the chemicals from a Danish ship, the Ark Futura.

The Cape Ray is expected to head into the open sea where it will neutralize the chemicals with special machinery outfitted in its cargo hole.

Danish vessel Ark Futura, foreground right, is moored next to the U.S.-owned MV Cape Ray, at Gioia Tauro port, southern Italy, Wednesday, July 2, 2014. (AP Photo/Vigili del Fuoco)

By late afternoon, about half of the 78 containers had been transferred, with cranes lifting each container onto a flatbed truck that then drove into the cargo hold of the U.S. cargo vessel MV Cape Ray.

Italy's environment minister, Gian Luca Galletti, proclaimed the mission a proud moment for Italy, tweeting that the country was contributing to international security in a "transparent and environmentally secure operation."

Local residents, however, complained that they were kept in the dark about what would happen and what chemicals were involved.

"You are killing us," read a banner held up by children, part of a small protest by residents concerned that the region's cancer rates could spike if any toxins leak.

Once all the chemicals - including mustard gas and the raw materials for sarin nerve gas - are transferred, the Cape Ray will sail into the open sea and begin the process of neutralizing the materials.

In the cargo hold are two Field Deployable Hydrolysis Systems: mazes of tanks, tubes, cables and electronics that will mix the chemicals with heated water and other chemicals in a titanium reactor to render them inert.

The resulting waste will be disposed of on land in dumps equipped to handle hazardous materials.

U.S. officials say no vapor or water runoff will be released into the atmosphere or the sea as a result of the process.