NATO told Syrian President Bashar al-Assad on Tuesday, December 4 that any use of chemical weapons in his fight against encroaching rebel forces would be met by an immediate international response, Reuters reported.

The warning from NATO Secretary-General Anders Fogh Rasmussen came as Syrian forces bombarded rebel districts near Damascus in a sustained counter-attack to stem rebel gains around Assad's power base.

International concern over Syria's intentions has been heightened by reports that its chemical weapons have been moved and could be prepared for use.

"The possible use of chemical weapons would be completely unacceptable for the whole international community and if anybody resorts to these terrible weapons I would expect an immediate reaction from the international community," Rasmussen told reporters at the start of a meeting of alliance foreign ministers in Brussels.

The chemical threat made it urgent for the alliance to send Patriot anti-missile missiles to Turkey, Rasmussen said.

The French Foreign Ministry referred to "possible movements on military bases storing chemical weapons in Syria" and said the international community would react if the weapons were used.

U.S. President Barack Obama on Monday told Assad not to use chemical weapons, without saying how the United States might respond. The Foreign Ministry in Damascus said it would never use such weapons against Syrians.