SANAA – The United Nations told its staff in Yemen to stay home on Monday, Oct. 7, a day after gunmen shot dead a German embassy security guard.

International humanitarian organizations have also advised staff to limit their movements, an aid worker said.

“Staff should remain at home and not travel. No travel to shops or elsewhere is approved. Tomorrow is uncertain and all Staff should be very cautious.” said an internal note sent by the U.N.’s Department of Safety and Security.

The German security guard was gunned down in Hadda district, in southwestern Sanaa, where the embassy is located. It was the latest in a series of attacks on foreign and local officials in the U.S.-allied state. No one has claimed responsibility.