BEIRUT, June 27 (Reuters) - Lebanese security authorities have arrested a senior executive at state-owned mobile telecom firm Alfa on suspicion of spying for Israel, security sources said on Sunday.

Army intelligence officials are questioning him. They have also arrested another 'valuable catch', one of the sources told Reuters, without elaborating.

The army has refused to comment. No one was available at Alfa to comment.

Lebanese newspaper ad-Diyar said army intelligence had arrested Alfa's head of transmissions and broadcasting with the charge of supplying Israel with sensitive information that harm Lebanese national security.

Ad-Diyar, which did not mention a source, said the executive was detained on Thursday and army intelligence officials were questioning him to find out who else had been working with him.

His job is a sensitive position because he is able to access information that few others can get, ad-Diyar said.

The sources did not identify the suspect's name to Reuters and ad-Diyar only released his initials as S. K.

Lebanon began a wave of arrests in April 2009 as part of an espionage investigation in which dozens of people have been arrested on suspicion of spying for Israel. A retired brigadier general of the General Security directorate was among the high profile detentions. More than 20 people have been formally charged.

Earlier this week a Palestinian refugee was also arrested.

Telecommunications in Lebanon are a sensitive issue. Politicians in the past have accused each other of eavesdropping on telephone calls.

The Western-backed government of former Prime Minister Fouad Siniora had accused Hezbollah in 2008 of violating Lebanon's sovereignty by operating a private telecommunications network, an accusation that in part sparked street fighting and brought the country to the brink of civil war.

Israel has not commented on any of the arrests.

Hezbollah, which fought a war with Israel in 2006, has called for the death penalty for all suspects convicted of spying for Israel.

Senior Lebanese security officials have said the arrests dealt a major blow to Israel's spying networks in Lebanon and that many of the suspects played key roles in identifying Hezbollah targets that were bombed during the 2006 war.

Other suspects have been charged with monitoring senior Hezbollah officials. A Lebanese arrested on suspicion of spying for Israel confessed in March to having helped in the assassination of a Hezbollah commander in 2004.