Lebanon officer suspected of spying flees to Israel

(Adds comment by U.N. Secretary-General, paragraphs 7-8)

BEIRUT, July 7 (Reuters) - A Lebanese army colonel suspected of collaborating with Israel fled to the Jewish state last week, a Lebanese security source said on Tuesday.

Two other Lebanese army colonels have been detained in a probe into spying for Israel that has led to more than 50 arrests. Around 20 of those detained have been formally charged.

The wave of detentions began in April with the arrest of a former brigadier general of the General Security directorate.

Lebanon has described the arrests as a major blow to Israel's intelligence-gathering in a country where it has fought several wars in the past 31 years, most recently in 2006 against Hezbollah guerrillas.

Hezbollah, which is backed by Iran and Syria, has called for the execution of those convicted. At least one of the suspects was involved in the 2004 assassination of Hezbollah commander Ghalib Awali, security officials have said. He was killed by a bomb in the southern suburbs of Beirut.

Lebanon has formally complained to the United Nations about its findings, saying the spying is a breach of a Security Council resolution that halted the 2006 conflict. There has been no official word from Israel.

In a regular report on Lebanon for the Security Council, issued on Tuesday, U.N. Secretary-General Ban Ki-moon said he was concerned at the Lebanese allegations of spying.

The allegations, "if proved, could endanger the fragile cessation of hostilities that exists between Israel and Lebanon," Ban wrote. (Additional reporting by Patrick Worsnip at the United Nations; Writing by Tom Perry; Editing by Charles Dick)