Saudi Arabia's foreign minister says Lebanon has been "hijacked" by Hizbollah and can only flourish if the political party and militia disarms.
Hizbollah was set up by Iran's powerful Islamic Revolutionary Guard the 1980s and has grown steadily in influence, sharing power in the Beirut government and giving crucial support to president Bashar Al Assad in Syria's civil war.
Its growing strength has alarmed Saudi Arabia and prompted - at least in part - the resignation of Lebanese prime minister Saad Hariri last month, though he has since decided to remain in his post.
"Lebanon will only survive or prosper if you disarm Hezbollah," Saudi foreign minister Adel Al Jubeir told a conference in Italy on Friday. "As long as you have an armed militia, you will not have peace in Lebanon."
Mr Al Jubeir said the situation in Lebanon was "tragic" and accused Iran of fomenting unrest across the Middle East.
"Since 1979, the Iranians have literally got away with murder in our region, and this has to stop," he said.
Riyadh ally Mr Hariri announced his resignation last month while in Saudi Arabia, triggering a political crisis in Lebanon that only calmed when he eventually returned to Beirut more than two weeks later.
Saudi Arabia has denied coercing Mr Hariri to quit.
Elsewhere in the region, Saudi Arabia fears that Hizbollah and Iran are trying to take control of its neighbour Yemen, by supporting the Houthi rebels against pro-government forces backed by a Riyadh-led military coalition.
Hizbollah denies fighting in Yemen, sending weapons to the Houthis, or firing rockets at Saudi Arabia from Yemeni territory. But on Friday Mr Al Jubeir rejected this and said his country would not back down in the conflict.
"The Houthis cannot be allowed to take over a country," he said.
Mr Al Jubeir said his country only had bad relations with two nations, Iran and North Korea, and that Riyadh did not have relations with Israel because it was waiting for a Palestinian peace deal.
He said everyone knew what a solution would look like to the Israel-Palestine conflict.
"It is not rocket science," he said, adding that he was waiting for the United States to put forward a new proposal.
One of the most intractable problems facing negotiators is the spread of Jewish settlements across occupied territory that the Palestinians want for a future state.
Mr Al Jubeir said he expected an eventual deal would set the borders of a Palestinian state on the lines prevailing before the 1967 war, when Israel captured the West Bank and Gaza Strip.
However, he said adjustments could be made for settlers: "Seventy per cent of the settlers who are on the (1967) Green Line remain in Israel, and the other 30 per cent - you offer them compensation and work out housing, and they can move to Israel."