Sen. John McCain Monday became the highest-ranking U.S. official to enter Syria since the bloody civil war there began more than two years ago, The Daily Beast has learned.

McCain, one of the fiercest critics of the Obama administration’s Syria policy, made the unannounced visit across the Turkey-Syria border with Gen. Salem Idris, the leader of the Supreme Military Council of the Free Syrian Army. He stayed in the country for several hours before returning to Turkey. Both in Syria and Turkey, McCain and Idris met with assembled leaders of Free Syrian Army units that traveled from around the country to see the U.S. senator. Inside those meetings, rebel leaders called on the United States to step up its support to the Syrian armed opposition and provide them with heavy weapons, a no-fly zone, and airstrikes on the Syrian regime and the forces of Hezbollah, which is increasingly active in Syria.

Idris praised the McCain visit and criticized the Obama administration’s Syria policy in an exclusive interview Monday with The Daily Beast.

“The visit of Senator McCain to Syria is very important and very useful especially at this time,” he said. “We need American help to have change on the ground; we are now in a very critical situation.”

Fighting across Syria has increased in recent weeks, with new regime offensives in several key areas, such as Damascus and the strategic border town of Qusayr. Thousands of soldiers serving Hezbollah—the Lebanon-based and Iran- and Syria-backed stateless army—have joined the fight in support of the regime, as the civil war there has threatened to ignite a region-wide conflagration and amid new reports of chemical weapons attacks by forces loyal to embattled president Bashar al-Assad this week that might cross President Obama’s “red line” for the conflict.

McCain’s visit came as the Obama administration is once again considering an increase of support to the Syrian opposition, while at the same time pushing the opposition council to negotiate with the regime at an international conference in Geneva in early June.

“What we want from the U.S. government is to take the decision to support the Syrian revolution with weapons and ammunition, anti-tank missiles and anti-aircraft weapons,” Idris said. “Of course we want a no-fly zone and we ask for strategic strikes against Hezbollah both inside Lebanon and inside Syria.”

There’s no assurance the Obama administration will be able to convince the Syrian opposition to attend the Geneva conference, and Idris said the conference would only be useful if there are certain preconditions, which the regime is unlikely to agree to.

“We are with Geneva if it means that [Syrian President] Bashar [al Assad] will resign and leave the country and the military officials of the regime will be brought to justice,” he said.

Prior to his visit inside Syria, McCain and Idris had separate meetings with two groups of FSA commanders and their Civil Revolutionary Council counterparts in the Turkish city of Gaziantep. Rebel military and civilian leaders from all over Syria came to see McCain, including from Homs, Qusayr, Idlib, Damascus, and Aleppo. Idris led all the meetings.

The entire trip was coordinated with the help of the Syrian Emergency Task Force, an American nonprofit organization that works in support of the Syrian opposition. Two leaders of the group attended all of the McCain-Idris meetings and discussed them with The Daily Beast.

The rebel troops are running low on ammunition and don’t have effective weapons to counter the regime’s use of airpower, the FSA and civilian leaders told McCain. They also said there’s a growing presence of Russian military advisers in Damascus as well as growing numbers of Iranian and Iraqi fighters.

Hezbollah has taken over the fight for the regime in Homs, they said. Estimates of Hezbollah’s presence there ranged from four to seven thousand fighters in and around city, outnumbering the approximately two thousand FSA fighters in the area.

The rebels also told McCain that chemical weapons have been used by the regime on multiple occasions.

“This was the start of a really important engagement between various forces in the U.S. government and people in the civilian and armed opposition who are working together to fight for a free Syria,” said Elizabeth O’Bagy, political director of the Syrian Emergency Task Force.

“Senator McCain proved today you can very easily go and meet with these people,” she said. “He’s the first U.S. senator to step foot in free Syria and one of the first government officials to reach out to the FSA officials and that’s a huge step.”

U.S. Ambassador Robert Ford is the only other high-ranking U.S. official to have entered Syria recently. He visited while on a trip to Turkey earlier this month.

The rebel leaders were appreciative of McCain’s visit but took the opportunity to communicate their unhappiness with what they see as a lack of crucial support from the Obama administration at a critical time in their struggle.

“They voiced their frustration at the policy of the U.S., because they believe that it’s in the interest of both the U.S. and Syria for the right people to be armed,” said Mouaz Moustafa, the Task Force’s executive director. “We need to increase the frequency of these types of visits by senior-level policy makers. It’s the best way to know who we are arming and to know who we are really dealing with.”

McCain, who also visited a U.S. Patriot missile site and met with U.S. forces there while in Turkey, declined to comment for this story. In an unrelated interview last week, he told The Daily Beast that he was concerned that the Geneva conference would only serve to give the regime more time to strengthen its military position against the rebels.

“I’ve been known to be an optimist, but here are the Russians sending them up-to-date missiles, continued flights of arms going into Syria, Putin keeps our secretary of State waiting for three hours … It doesn’t lend itself to optimism, all it does is delay us considering doing what we really need to do,” said McCain. “The reality is that Putin will only abandon Assad when he thinks that Assad is losing. Right now, at worst it’s a stalemate. In the view of some, he is succeeding.”