Iran's announcement of the second network of centrifuges in its uranium enrichment process is a "negative signal", Jean-Baptiste Mattei, spokesman of the French Foreign Ministry said on Friday.

The Iranian announcement "aggravates the worries of the international community" and sends a "negative signal which we should take into account in our evaluation of the dossier," Mattei told a news conference.

The door is always open to negotiations, if Iran decides to "return to the negotiation table", Mattei said, noting that the priority goes to the negotiations for a UN Security Council resolution.

Mattei made the remarks after Iranian reports said that the country had begun feeding gas into a second cascade of centrifuges to enrich uranium.