Egypt's interior ministry said that a "loud explosion" that created panic in downtown Cairo on Wednesday was caused by a sonic boom by a low flying aircraft.
"The sound of the explosion in the (southern neighborhood) of Maadi and in central Cairo was the sound of a plane that broke the sound barrier," the ministry said in a statement.
"We have received reports from several citizens who say they heard a loud explosion," in different parts of the city, Mohsen told MENA, in statements broadcast on television when the boom was first reported.
"Security services have been sent to the various areas to investigate the reports," he said.
The sound of the blast shook windows in Maadi and was heard as far away as northern Cairo, residents told AFP.
The country has been held in the grip of unrest since the ouster of long-term president Hosni Mubarak in February, which saw power handed to the Supreme Council of the Armed Forces.
Last week, bloody clashes erupted between protesters and anti-riot police in Cairo's Tahrir Square amid mounting frustration with the country's military rulers and a sweeping victory by hardliner Islamic parties in Egypt's parliamentary polls.
Some observers say Egypt's caretaker junta could have ordered the sonic boom as a form of psychological warfare aimed at unsettling protesters - and as a warning not to escalate challenges to their rule.
Egypt's economy has lost some $8.9 million in net cash outflows during the past 11 months of unrest - and has burned through nearly half of its foreign currency reserves. It has also seen its credit downgraded as pledges for foreign aid have been held up due to the ongoing unrest.