U.S. counterterrorism officials warned local law enforcement and emergency personnel to beware of suspicious packages that might contain dangerous substances, Fox News Channel confirmed Monday.

The Department of Homeland Security (DHS) and the FBI sent out a bulletin Sunday, warning local officials to scrutinize packages with unusual characteristics, no return address and excessive postage.

The advisory comes after two U.S.-bound packages posted in the Yemeni capital Sanaa were intercepted on UPS and FedEx freight planes in Dubai and East Midlands Airport in the U.K. Friday. The parcels were found to contain powerful explosives hidden inside printer toner cartridges.