As tension grows between Israel and Hezbollah, the dominant political and military force in Lebanon, neither side wants a full-scale war. But one could explode inadvertently — precipitated by an attack like the launch of what Israel said was a Hezbollah missile that hit Majdal Shams in the Golan Heights on Saturday, for example — or deliberately, should Israel see a post-Gaza opportunity to rid itself of another one of its enemies.

In the best case, a cease-fire in Israel’s war on Hamas in Gaza would prompt Hezbollah to stop firing rockets into the Jewish state, and the possibility of war would fade.

After Saturday’s missile strike, which killed 12 children and teenagers, Israel hit a building in Beirut on Tuesday, saying it targeted the Hezbollah commander it believes was responsible. If Israel goes further and launches a major operation to uproot Hezbollah, which right-wing members of Prime Minister Benjamin Netanyahu’s government have been urging, it would be devastating.

The conflict would eviscerate Lebanese society, which is already in a state of economic collapse, spark a humanitarian crisis for which the United States and others will have to pick up the tab, generate increased attacks against U.S. interests in Iraq, Syria and elsewhere, and propel violence by Houthi forces in Yemen to higher levels. It will likely also fail to eliminate Hezbollah.

None of this is in the United States’ interest. While making clear that it would continue to defend Israel against direct attacks by Iran, Hezbollah’s patron, Washington needs to make clear to Israel that it will not sanction such a war or facilitate it by supplying munitions, joining the Israeli military in attacks against Hezbollah or providing diplomatic cover for the deaths of civilians.

As the conflagration in Gaza demonstrated, trying to control this train after it has left the station will not work.