Ousted president Hosni Mubarak's sons on Sunday were questioned on their financial activities in Cyprus and the British Isles, the public prosecutor's office said.
Alaa and Gamal Mubarak faced investigators at the Cairo prison where they are being held after the interior ministry refused to transfer them "for security reasons," a spokesman at the office said.
The interrogation focused on their ties "with a company in Cyprus and one of the British Isles managing investment funds of some businessmen," he added, without elaborating.
Both men are also accused of forcing businessmen to give them a cut in local partnerships with foreign companies.
The two were on Wednesday ordered detained for 15 days in Cairo's Tora prison complex as part of a probe into the violent suppression of anti-regime protests which led to Mubarak's fall and over corruption accusations.
Before the popular uprising which ousted Mubarak, Gamal, who was close to business executives and high up in Egypt's ruling party, was regarded as the political heir to Mubarak, while Alaa concentrated on business.