A menacing message from Ahmadinejad....

Hezbollah keeps on growing in power...

But it is Hizbollah's continued – though constantly denied – involvement in terrorism, rather than its confrontational posture with its southern neighbour, that is the real motivation behind Mr Ahmadinejad's decision to become the first Iranian president to visit the region.

In a few weeks' time, the United Nations special tribunal that has spent the past five years investigating the assassination of former Lebanese prime minister Rafik Hariri is due to publish its findings. Mr Hariri, a self-made Sunni Muslim billionaire who was financing Lebanon's post-civil war reconstruction, was killed by a car bomb as he drove through Beirut in 2005.

Lebanese security officials immediately suspected Hizbollah because Mr Hariri was demanding that the party disband its militia and arrange for its thousands of fighters to join up with Lebanon's conventional armed forces. The bombing also bore all the hallmarks of Imad Mugniyeh, who masterminded the 1980s Beirut lorry bombings and who was himself killed by a car bomb in Damascus in 2008.

Details of the UN tribunal's findings leaked to the Beirut press suggest that, apart from Mugniyeh, the investigators have uncovered evidence that links as many as 50 senior Hizbollah officials to the assassination. This includes intercepts of mobile phone calls made between Hizbollah officials in the days leading up to Mr Hariri's murder.

In an attempt to distance the organisation from the report's conclusions, Shiekh Hassan Nasrallah, the Hizbollah leader who lives in permanent hiding for fear of assassination by Israel, issued a video statement in the summer claiming that those involved with Hariri's assassination were "undisciplined members which the group has no relations with".

Diplomatic sources in Beirut tell me that, to avoid a confrontation between Hizbollah and the Lebanese government, Saad Hariri, the current prime minister and son of the murdered politician, has offered Nasrallah a deal whereby the assassination is blamed entirely on Mugniyeh, who is no longer in a position to face criminal prosecution. But Nasrallah, who regards Mugniyeh as a "martyr" to Hizbollah's cause, has refused, and is trying to pressure Mr Hariri to reject the findings of the UN investigation.

This is a hard ask for a man who saw his father blown to pieces by a car bomb. It is also a totally unacceptable proposition for the millions of Christian and Sunni Muslim Lebanese who oppose Hizbollah's attempts to impose its uncompromising Islamic ideology on their lives.

By parading through Shia-dominated southern Lebanon yesterday, Mr Ahmadinejad was not only demonstrating his loyalty to Tehran's favourite Islamic militia. He was also sending an uncompromising message to Mr Hariri's government to drop the charges against Hizbollah, or face the consequences.