Updated

U.N. Secretary-General Ban Ki-Moon is urging the Syrian government to accept an expanded U.N. probe into alleged chemical weapons use, saying he has concluded that an alleged attack in Homs in December warrants investigation.

Syria on Monday rejected the expanded investigation, which it had originally sought to look into alleged use of chemical weapons by rebels in March on the village of Khan al-Assal. The rebels blame regime forces.

Britain and France asked the U.N. to investigate allegations of chemical weapons use in Khan al-Assal and another village, Ataybah, on March 19, as well as Homs on Dec. 23.

Speaking Tuesday in Rome, Ban said he decided the mission should also look into the Homs allegations and urged Syria to "extend its fullest cooperation and allow the investigation to proceed."