An unknown caller prank called Britain's Prime Minister Sunday resulting in a call for a government review. 

The prankster called Prime Minister David Cameron Sunday pretending to be one of the country's top spy chiefs at GCHQ, according to CNN. The Government Communications Headquarters is a British Intelligence Agency and they received a prank call prior to the prime minister.

A government spokeswoman said the caller received a mobile phone number for the Director of the agency, which is never used for calls involving classified information. The second caller placed a call to the prime minister pretending to be the director. The spokeswoman said classified information was not disclosed in either conversation. 

Great Britain has heightened level of security due to the possibility of terrorist threats, according to The Wall Street Journal. Cameron ended the call as soon as he realized it was a hoax. But the calls represent an embarrassing lapse in security during a tense time. 

A notice went out to all departments to be on alert for more prank calls, and authorities said they are reviewing procedures to ensure that those types of calls do not occur again, CNN reported. 

No one has claimed responsibility for the calls and it remains unclear if the two calls are related, The Wall Street Journal reported. 

This is not the first time a British intelligence agency has received prank calls. Number 10 used to receive calls in the past. The last time Number 10 received a hoax call was in 1998 from a radio DJ pretending to be an opposition leader. The radio DJ was patched through to former Prime Minister Tony Blair.