If you need proof that Mahmoud Ahmadinejad wants to plant the Revolutionary Iranian flag in Jerusalem, consider this. A replica of the Al-Aqsa mosque is being constructed by Iran in southern Lebanon as a prop for Ahmadinejad’s visit next week. The Iranian president will officially open the mosque for business and be photographed in front of it throwing stones toward Israel. And the mosque, according to Israeli reports, has the flag of Iran flying over it.

Hezbollah has flown Iranian flags in southern Lebanon for some time. The terrorists operate an Iran-sponsored fiefdom there; UNIFIL has been unable for months to conduct patrols in towns denied to it by Hezbollah, a pattern repeated this past weekend when the UN force sought to investigate a Hezbollah weapons cache in its patrol zone.

But Iran and Hezbollah have chosen to take advantage until now of the minimal independent news coverage in southern Lebanon. Little gets into the Western press about the situation there, and when it does, it doesn’t come from Hezbollah or Iran. What Ahmadinejad plans to do next week, with media coverage and pointed images, marks a major “informational” break. It’s a plan to draw back the veil and clarify Hezbollah’s loyalties and Iran’s involvement. And the central theme is the Iranian flag symbolically aloft over Jerusalem.

This blatant signal is something Ahmadinejad should be prevented from sending. It will be as much a shot across Saudi Arabia’s bow as across Israel’s: a symbolic announcement that the “race to Jerusalem” is on. As discussed here, the Saudis — default leaders of the Arab world — already show signs of preparing to compete in that race.

Unfortunately, the fecklessness of the UN extends beyond an impotent UNIFIL. The UN Special Coordinator for Lebanon, British diplomat Michael Williams, met with an Iranian envoy last week to discuss the visit by Ahmadinejad and approved it as a “significant event.” He went on to hail “Tehran’s balanced approach and inclusive relations with all political and religious parties in [Lebanon].” The UN will not be a source of responsible diplomacy; neither will Russia, which is positioning itself to back the winner of the race to Jerusalem. The EU remains mired in domestic constituency tending, and therefore focused on the legal status of Gaza flotillas and the arguing of anti-Israel resolutions in Brussels.

Among the Middle East Quartet, only the U.S. retains such a posture as would make it possible to take action against the beginning of a “race to Jerusalem.” The pressure point is the government in Beirut, which, if it accepts Ahmadinejad’s visit, must exercise its formal sovereignty over the southern territory and ensure that no Iranian flags are flown over anything but Ahmadinejad’s official convoy. Israel is pressing the Lebanese to cancel the visit; if the U.S. cannot bring itself to do that, our diplomats should at least embolden the Lebanese to get the Iranian flags out of there. This is not meaningless symbolism. The fact that it’s Ahmadinejad and Hezbollah who feel emboldened at present is the most meaningful one of all.