The staff of the organisation also observrd a minute of silence to express solidarity with the families and friends of their colleagues killed in the Gaza conflict, Xinhua reported.
"In less than one month of military conflict, the UN Relief and Works Agency (UNRWA) lost eleven of its personnel in Gaza," said UN deputy spokesperson Farhan Haq.
Other than nine fallen staff members of the agency, two UNRWA contractors employed under its job creation programme were killed while on duty in its shelters, according to the spokesman.
"In addition, in recent years, twelve people working for the agency have died in Syria, in addition to one who died in the West Bank," Haq added.
At an informal meeting of the UN General Assembly on Wednesday, UN Secretary-General Ban Ki-moon thanked the staff for their bravery and stressed that attacks against UN premises, along with other suspected breaches of international law, must be swiftly investigated.
According to the UN, the agency's schools and other buildings have been used as temporary shelters for some of the nearly 270, 000 displaced people throughout the Gaza Strip. On Aug 3, a third school in ten days was hit.