The British embassy in Cairo remained closed Monday amid ongoing fears over security, the foreign office said.
Britons in Egypt will be unable to apply for visas and some will face delays in getting passports returned as public services are stopped, BBC reported.
The embassy was initially closed Sunday, but the exact nature of the security risk has not been confirmed.
This closure is to "ensure the security of the embassy and our staff", British Ambassador to Egypt John Casson said.
"Public services at the British embassy are currently suspended. We are working to restore full services as quickly as possible and to keep British nationals in Egypt and other customers informed," he added.
"I am grateful for the close and ongoing cooperation with the Egyptian government to achieve this."
A warning on the Foreign and Commonwealth Office (FCO) website said: "Please do not come to the embassy building."
It also said that the British consulate in Alexandria in the north of Egypt was open as usual.
"There is considered to be a heightened threat of terrorist attacks globally against UK interests and British nationals from groups or individuals motivated by the conflict in Iraq and Syria," the FCO said in its online travel advice for Egypt.
"You should be vigilant at this time. Terrorists continue to plan attacks in Egypt. Attacks could be indiscriminate and occur without prior warning," it added.
"Foreigners could be targeted in tourist resorts or other locations frequented by foreigners. Previous attacks have almost exclusively targeted the security forces, their facilities and other government buildings."
However, popular tourist destinations along the Nile river, including Luxor and Red Sea resorts such as Sharm el Sheikh are not mentioned in the advice.
