"There is a risk of course of dragging out, and we can see the tactics of the regime that is to buy time," France's foreign minister, Alain Juppe told reporters on the sidelines of the second "Friends of Syria" conference in Istanbul on Sunday.
"This is why we must, and we did all agree, to set a time limit for this plan" of Annan, he added.
Annan's plan calls for an end to the violence, a daily two-hour humanitarian ceasefire and access to all areas affected by the fighting in Syria, as well as an inclusive Syrian-led political process, a right to demonstrate, and the release of those detained.
President Bashar Al-Assad said he accepted the plan Tuesday, without halting shelling of opposition strongholds. Annan is not attending the conference and Russia and China, Damascus's two remaining major allies, have also opted out.