By Ehab Farouk and Mirette Magdy

CAIRO, June 16 (Reuters) - Egypt's financial market regulator is examining share trades made by a board member at Beltone Financial two days before Beltone bid for a stake in investment bank EFG Hermes, two people familiar with the matter said.

Beltone has joined up with billionaire Naguib Sawiris to bid $257 million for a 20 percent stake in EFG Hermes, one of the biggest investment banks in the Middle East.

The offer, submitted to the Egyptian Financial Supervisory Authority (EFSA) on June 5, suggests a potential revival of dealmaking in Egyptian equities after more than three years of stagnation following the overthrow of Hosni Mubarak in 2011.

"One member of Beltone's board of directors bought more than 255,000 EFG Hermes shares in his own name and that of a company belonging to him over two days before the formal offer was presented to the financial regulator," one of the sources said.

"A sister of another board member at Beltone also bought (shares) two days before the offer and the financial regulator is looking into the case," the source added.

The sources said the deals being investigated were made between June 2 and 3 and the two individuals had bought further EFG Hermes shares one day before the June 5 announcement.

Those subsequent purchases did not go through because the stock exchange decided to cancel all prior-day trading in EFG Hermes when the bid was announced.

Egypt financial market rules prohibit share trading based on information that is not available to the public. The stock exchange monitors the market and tips off EFSA when it suspects insider dealing.

EFSA Chairman Sherif Samy said: "We do not comment on the validity of any transactions in the market that are under suspicion".

Shares in EFG Hermes have risen from around 13 Egyptian pounds before the announcement of the share offer to close at 15.28 pounds on Sunday. The stock was down 0.7 percent at 15.26 pounds on Monday.

A person at Beltone who declined to be named said the non-executive board member who bought shares in EFG Hermes ahead of the formal announcement was not aware of Beltone's share offer before a board meeting on June 4.

"Only the executives in Beltone's board of directors were aware of the offer," he said. ($1 = 7.1501 Egyptian Pounds) (Writing by Asma Alsharif; editing by Tom Pfeiffer)