For more than a year now, the United States has been walking a fine line in Syria's civil war, offering rhetorical support and non-lethal aid to the anti-Assad rebels, while publicly distancing itself from any notion of deploying American military power to topple the regime in Damascus.

In the latest push to seek a negotiated settlement to the conflict, the US and Russia have agreed to sponsor talks between the fragmented rebels and President Bashar al-Assad's regime in Geneva, possibly as early as June.

But the key differences between the two Security Council members remain. The US continues to push for Assad to step down, while Russia considers his fate an internal Syrian issue. Peace talks have also been complicated by Moscow's call for Iran, Washington's main rival in the region, to participate in the negotiations.

In the US Congress, key senators are putting little stock in the push for peace and are calling for direct US intervention on the ground. The scenarios range from arming the rebels, to establishing no-fly and safe zones, to intervening with ground troops to secure the Assad regime's chemical weapons stockpiles.

Defense Secretary Hagel has expressed deep skepticism about intervening in Syria

"We have an obligation and responsibility to think through the consequences of direct US military action in Syria," US Defense Secretary Chuck Hagel told the Senate Armed Services Committee last month.

"Military intervention at this point could hinder humanitarian relief operations. It could embroil the United States in a significant, lengthy and uncertain military commitment," Hagel said.

Arming the rebels

Senators Robert Menendez and Bob Corker have drafted a bill that would give President Obama the authority to begin arming select rebel factions. Currently, the administration has publicly agreed to send only humanitarian and non-lethal aid to the opposition.

"To change the tipping point in Syria against the Assad regime, we must support the opposition by providing lethal arms and help build a free Syria," Menendez said.

"Vital national interests are at stake and we cannot watch from the sidelines as the Iranian presence in Syria grows, a growing refugee crisis threatens to destabilize the region, chemical weapons are used against the Syrian people, and al Qaeda-affiliated groups take root there," he added.

According to Menendez, only vetted rebel groups "that meet certain criteria on human rights, terrorism, and nonproliferation would be eligible" to receive US arms. And the transfer of anti-aircraft weapons would be subject to strict limitations.

The White House is concerned weapons could fall into the hands of Islamists

The Obama administration is already facilitating the third-party transfer of arms from Eastern Europe to some Syrian rebel factions, according to Aram Nerguizian with the Center for Strategic and International Studies.

There has been concern in both Congress and the White House that weapons could end up in the hands of Islamist militants, like the al Nusra front, and later be used against US interests. Nerguizian said that preventing the proliferation of weapons would be a difficult task in Syria's chaotic environment, particularly at checkpoints where different rebel factions often pilfer arms from each other.

"The reality is that there's very little likelihood that any one faction will be so wedded to the idea that they need to protect what are fundamentally alien US interests in such a scenario," Nerguizian, an expert on strategy in the Mideast, told DW.

"It's far more likely that you will have at least of some leakage of weapons, whether they're US or otherwise," he said

Calls for no-fly, safe zones

Since the early stages of Syria's civil war, there have been calls in Western countries for the establishment of no-fly and safe zones for the opposition. Last March, Senators Carl Levin and John McCain wrote a letter to President Obama, calling on him to use "limited" military force to establish sanctuaries inside Syria.

"We urge you to lead an effort, together with our friends and allies, to degrade the Assad regime's airpower and to support Turkey if they are willing to establish a safe zone inside of Syria's northern border," the senators wrote.

But according to Nerguizian, that kind of military operation would likely require two carrier battle groups, each of which includes an aircraft carrier and their accompanying support ships.

Senator McCain has called for arming the rebels and establishing a no-fly zone in Syria

"You're talking about around the clock operations to suppress Syrian air power and anti-air capability, and as the battle of Qusair has shown, it's dangerous to underestimate Assad's military," Nerguizian said. The Syrian government fought over the weekend to retake the city of Qusair, which lies on the road to northern Lebanon and the Mediterranean Coast.

A Western military operation involving carrier groups would also be complicated by the fact that Russia has deployed five additional navy ships to the Mediterranean. Moscow has also sold anti-ship missiles to Syria. Those missiles are capable of striking vessels as far away as Cyprus.

Securing Syria's chemical weapons

Defense Secretary Hagel told the Senate Armed Services Committee that some 200 US military personnel had been sent to Jordan to help plan for potential operations related to Syria's civil war. The Los Angeles Times reported that the number could be increased to 20,000, if the Obama administration decided to intervene to seize Syria's chemical weapons.

But a CNN report in February, citing an unnamed Pentagon official, said that such an operation would require up to 75,000 ground troops. Nerguizian says that regardless of the talk of military intervention, at some point - sooner or later - negotiations will be necessary.

"At some point, by force or through fatigue, there's going to be a need for a political process," he said. "And you are going to need the kind of international support for a renegotiation of power in Syria that ended the Lebanese civil war."