BEIRUT, Lebanon — Saudi Arabia said Friday that it was stopping payment on $4 billion worth of military aid and other support for the army and security services of Lebanon because the country did not condemn attacks on Saudi diplomatic missions in Iran.

The decision was a new step in the proxy war between Saudi Arabia and Iran, who are on opposing sides in the wars in Yemen and Syria and competing for influence elsewhere across the Middle East.

Lebanon, with its diverse sectarian composition, has long been a battleground for the two regional powers, with Shiite Iran bankrolling Hezbollah, the Lebanese militia, and Sunni Saudi Arabia supporting opposing political parties and figures.

But Saudi influence has waned in recent years as its preferred politicians have lost influence in Lebanon, and Hezbollah has emerged as the country’s most powerful military force.