Spying is as familiar in Beirut as it was in post-war Vienna – there's even a giant "Third Man"-type ferris wheel here – but the events of the last few days are growing more mysterious by the hour. Over the past two weeks, a special unit of Lebanon's Internal Security Force (ISF) has been arresting a clutch of Lebanese allegedly working as spies for Israel.

There are least 21 men and one woman under interrogation and the ISF has been regaling us all with the highly sophisticated Israeli communications equipment found hidden at their homes.

Those detained include a local journalist in the Bekaa Valley and a senior officer in the Lebanese army, a man who was wounded by Islamist gunmen at the battle of Nahr el-Bared in 2007. They've even picked up a retired general and his wife. Colonel Maurice Diab is a much respected soldier, although military officers say that questions were first raised some time ago when he was sent for training to the United States on a government grant but in a photograph taken on the course could be seen standing next to uniformed Israeli officers. He lives in the north Beirut coastal suburb of Antelias, although other arrests are spread across eastern Lebanon and the border village of Rmeish.

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So far so good. But it is becoming increasingly obvious that some of the "intelligence" behind these detentions – and more than 50 people in all have so far been questioned – came from the Shiite Hizbollah, who are, of course, Syria's and Iran's best friends in Lebanon. This comes just a couple of weeks after four senior pro-Syrian Lebanese security officers were released from jail after being held on suspicion of helping to plan the assassination of ex-prime minister Rafiq Hariri and 21 others in 2005. So are the intelligence authorities in the country back to their old tricks of hooking up with Hizbollah?

This is not an idle question, because Sayyed Hassan Nasrallah, Hizbollah's chairman, is now demanding that Lebanese "collaborators" of Israel be executed. Mr Nasrallah, it should be remembered, is the man who kicked off a war with Israel in 2006, in which more than a thousand Lebanese were killed, and then called it a "divine victory".

He enraged many Lebanese even more last week by describing the Hizbollah's temporary armed takeover of West Beirut last year as a "glorious day", even though dozens of Lebanese were killed.

Indeed for Sunni Muslims and a good many Christians, Mr Nasrallah – who appears on a giant Big Brother screen at Hizbollah rallies, speaking from his various hiding places – is talking as if he is the president of Lebanon rather than the actual office holder, the ex-general Michel Suleiman. Add to this the growing belief that the Lebanese opposition, whose backbone is Hizbollah, might win next week's national elections, and the arrest of an Israeli spy network takes on a much darker complexion.

The Israelis have indeed been trying to re-recruit some of their former Lebanese collaborators in order to re-establish their intelligence service there after their debacle in the 2006 Hizbollah war. The best sources say that some of these men worked for Israel before the Israeli army left Lebanon in 2000 and that several of them turned the Israeli offer down flat while others actually informed the Lebanese authorities of the approach from Israel and may even have snitched to them on the identity of the men and the woman who have just been arrested.

Now the Americans are gently warning that if Hizbollah and its chums, including the Christian former General Michel Aoun, win the elections, it will have to "re-examine" its aid package to Lebanon which includes substantial, though largely out-of-date, equipment for the Lebanese army. "Why are you worried?" Mr Nasrallah asked another of his interminable rallies last week. "Iran and Syria can give equipment to the Lebanese army."

The pot has now been further stirred by an incendiary and highly contentious article in Der Spiegel. It reported that the UN Tribunal set up in the Hague to find ex-prime minister Hariri's killers – the same tribunal that ordered the four generals released two weeks ago – is focusing on Hizbollah as the potential murderers. A lie, says Mr Nasrallah, an "Israeli plot". The tribunal says it gave no such information to the German magazine. And sure enough, Israeli defence minister Ehud Barak has now warned the world that if Hizbollah and its allies win the elections, Israel will have "greater freedom of action". Not without more spies it won't.

Israel's intelligence performance in 2006 was lamentable. It turned out that Hizbollah had actually got their hands on Israel's own aerial photo-reconnaissance pictures of Lebanon, clearly showing which of Hizbollah's bunkers had been identified and which had not. If this latest spy network is real, the Israelis are not going to do much better next time round.