Arab states will not accept a new international envoy to Syria after Kofi Annan's resignation unless his or her mandate is to clearly negotiate a transfer of power, Qatar's prime minister said on Saturday.

"Arab nations will not accept a new envoy with the same mandate that was given to Annan," Sheikh Hamad bin Jassem al-Thani told Al-Jazeera of the outgoing UN and Arab League envoy, whose six-point plan for peace was never implemented.

"The only acceptable designation is working on the peaceful transfer of power in Syria."

Sheikh Hamad said he had contacted UN Secretary General Ban Ki-moon, Arab League chief Nabil al-Arabi and Annan himself to inform them of this decision.

"The six-point plan is over," he said.

He said any new envoy must be tasked with working on "the peaceful transfer of power in Syria" and must follow a new strategy after the "failure" of the Annan plan.

"The plan must clearly be modified" after "none of it was implemented."

Annan announced his resignation on Thursday after violence intensified across the war-torn country, where a rights watchdog estimates that more than 20,000 people have been killed since March 2011.