Doctors Without Borders (MSF) suspect chemical weapons in use in Syria

Medecins Sans Frontieres says hospitals it supports in Syria treated about 3,600 patients with "neurotoxic symptoms", of whom 355 have died.

It said the patients had arrived in three hospitals in the Damascus governorate on 21 August - when opposition activists say chemical attacks were launched against rebels.

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"MSF can neither scientifically confirm the cause of these symptoms nor establish who is responsible for the attack," said MSF Director of Operations Bart Janssens.

"However, the reported symptoms of the patients, in addition to the epidemiological pattern of the events, characterised by the massive influx of patients in a short period of time, the origin of the patients, and the contamination of medical and first aid workers, strongly indicate mass exposure to a neurotoxic agent.

If claims that Syria used chemical weapons this week are true, a speedy response will be needed to prevent another such attack, U.S. Defense Secretary Chuck Hagel said.

Hagel's comments Friday came after a senior Defense Department official told CNN that military planners have updated Syrian target lists.

And it was disclosed that a fourth U.S. ship armed with cruise missiles has arrived in the eastern Mediterranean Sea.