Secretary-General Ban Ki-moon is again appealing to Syria to allow a team of experts into the country "without delay and without any conditions" to investigate allegations of chemical weapons use.

The U.N. chief told reporters Monday he takes seriously a recent U.S. intelligence report which indicated Syria has twice used chemical weapons.Syria wants any investigation limited to an incident near Aleppo in March but Ban wants a broader investigation, including a December incident in Homs.

Ban stood beside Swedish chemical weapons expert Ake Sellstrom, who heads the team, which he praised for its "integrity and independence and professionalism."

The team is already gathering and analyzing available evidence, but Ban said onsite activities are essential if the U.N. is to establish the facts and "clear all the doubts."