Saudi Arabia's foreign minister says his country views the involvement of Iran and Lebanese Shi'ite militant group Hizballah in Syria's civil war as dangerous.
Prince Saud al-Faisal added that Riyadh "cannot be silent" about Tehran's role in Syria.
He was speaking at a joint news conference with U.S. Secretary of State John Kerry in Jeddah.
Faisal also said that Syrian rebels must be offered military aid and called for measures to stop Iran and Hizballah from supporting the Syrian government.
"Syria is facing a massive flow of weapons to aid and abet that invasion and that genocide. This must end," Faisal said.
Kerry refused to talk about the kind of weapons that might be provided to the Syrian opposition but backed the Saudi call for reining in Iran and Hizballah.
"But we will continue to provide assistance to the Syrian military coalition and to the Syrian opposition in the interim, because we do not believe it is appropriate for the Assad regime to have invited the Iranians and Hizballah to cross international lines and to have their fighters on the ground," Kerry said. "There are no United States fighters. There are no Saudi fighters. There are no Qatari fighters on the ground."
Kerry said that Washington remains convinced that an international conference offers the best chance to bring about a negotiated political settlement.
But Lakhdar Brahimi, the UN and Arab League envoy for Syria, has said that a second peace conference is unlikely to happen soon.
"Frankly, I now doubt whether the conference [on Syria] will take place in July," Brahimi said. "The opposition -- I think their next meeting is on July 4 and 5 -- so I don't think they will be ready."
The UN says Kerry and Russian Foreign Minister Sergei Lavrov will meet next week after senior officials from the two countries failed on June 25 to set a date for the proposed conference.
Brahimi urged international unity and cooperation to prevent the Syrian conflict from spiraling into a much bigger disaster.
"What is happening in the region is extremely, extremely serious," he said, "and I very, very much hope that governments in the region and the big powers, particularly the United States and Russia, I'm sure they are aware, that they will act to contain this situation that is getting out of hand."
More than 93,000 people have been killed in the Syrian conflict, which began in March 2011 as a popular protest movement against the regime of President Bashar al-Assad.
After a harsh government crackdown and the opposition reverting to armed struggle, the conflict in Syria descended into a civil war with sectarian overtones.
Some 1.7 million Syrians have fled into neighboring countries.
With reporting by Reuters and dpa