CAIRO, April 8 (Reuters) - The chairman and three senior executives of Egyptian mobile firm Mobinil were ordered jailed on Monday for illegally re-routing international phone calls via a transmitter near Egypt's border with Israel, making it easier to intercept them, officials said.

The economic misdemeanor appeals court upheld a three-year prison term for Mobinil chairman Iskander Shalaby and sentences of five years each for three other senior managers.

Mobinil, one of Egypt's three mobile operators, was also ordered to pay fines totaling more than 460,000 Egyptian pounds ($67,200) to the telecommunications authority.

The state prosecutor sent the Mobinil executives to trial last year for violating licensing conditions by modifying a Mobinil transmitter in the Sinai Peninsula near the frontier with Israel without the telecom authority's permission.

A lower court ruling last May stated that alterations to antennae on the transmitter violated official regulations.

The court found that the signal from the station exceeded legal levels, suggesting that incoming calls to the border transmitter originating from outside of Egypt were amplified.

The ruling did not say explicitly that the transmitter enabled Israel to monitor international phone calls with Egypt.

However, state-owned Al-Ahram newspaper reported at the time that the prosecution had argued the altered transmitter allowed a strong signal to be accessible inside Israeli territory, allowing Israel to monitor and record Egyptian calls.

Mobinil said in a statement on Monday that its officials had not acted illegally and the company would appeal to Egypt's highest court of cassation.

France Telecom owns 94 percent of Mobinil, Orascom Telecom Media and Technology Holding owns 5 percent, and only the remaining 1 percent is listed on the exchange, according to Mobinil's website. ($1 = 6.8490 Egyptian pounds) (Reporting by Asma Alsharif and Maggie Fick; Editing by Paul Taylor and Mark Heinrich)