The ad was placed by the Anti-Defamation League, a US organisation that monitors anti-Semitic activity around the world. The ad said: "Israel we are with you. Now more than ever", and appeared on page seven of Friday's Herald Tribune, which publishes an edition in Beirut.
Lebanese laws prohibit the publication of pro-Israeli material as the country is, in name at least, still at war with Israel. Israel only pulled out of Southern Lebanon last year after 20 years, having taken control of the area in a bid to halt attacks by Islamic Hezbollah terrorists.
The Associated Press has reported that Lebanese Prosecutor General Adnan Addoum has decided to proceed with a case against the Herald Tribune, after consulting with the country's information minister, Ghazi Aridi.
Punishment could be a fine of around 1m Lebanese pounds (£450) or even a prison sentence for the Herald Tribune's Lebanese representative. However, the Lebanese government would need to prove that there had been intent to cause insult.
The Herald Tribune is jointly owned by the New York Times and the Washington Post.
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