Egypt's foreign ministry sharply criticized the US Embassy in Cairo for advising citizens to avoid large gatherings in the capital until Sunday, calling the move "unjustifiable".The largest Arab nation is currently battling an Islamist insurgency mainly concentrated in the Sinai Peninsula and which gained pace after its military ousted President Mohamed Mursi, an Islamist, in 2013 after mass protests against his rule. There have been occasional militant attacks in Cairo and other cities.The US Embassy's message warned against being in public spaces, near diplomatic missions, government buildings, and transport hubs. It cited "potential security concerns" but did not specify what they were."The foreign ministry spokesman has conveyed his annoyance at the warning released by the United States embassy in Cairo to Americans," the ministry said in a statement. "(This) raises questions over the reasons this statement was released in such a way."The ministry said it contacted the embassy over the warning and that it was told there were no specific reasons or threats behind the move. The ministry quoted the embassy as telling it that the warning was a routine measure taken every time there is a long weekend and thus more crowding in public areas.Thursday was a public holiday in Egypt in celebration of Armed Forces Day. The Egyptian weekend is Friday and Saturday.The foreign ministry said it expressed dismay to the embassy because such "unjustifiable warnings" could have negative effects especially on the economy. It cautioned all embassies in Egypt against "releasing unjustified" warnings. The British and Canadian embassies had issued similar warnings to avoid public gatherings until Sunday but were not specifically mentioned in the statement.The insurgency, mounted by Islamic State's Egyptian branch Sinai Province, has killed hundreds of soldiers and police and begun to attack Western targets within the country.The attacks have dented the recovery of tourism after a 2011 uprising drove away tourists, a major source of hard currency. Import-dependent Egypt is facing a dollar shortage that has stifled business activity and hit confidence in the economy.