Two senior members of the US Senate Armed Services Committee urged international cooperation to help supply anti-Assad rebels with weapons and other aid on Monday.
Both Arizona Sen. John McCain and Sen. Lindsey Graham of South Carolina, however, stopped short of endorsing direct US intervention as Syrian tanks and reinforcement roll towards Homs.
"The United States doesn't have to directly ship weapons to the opposition, but there are a whole lot of things that can be done" through groups such as the Arab League, McCain told reporters.
Graham said it was "shameful" for the US not to have a prominent role to help the rebel forces, saying that breaking Syria's ties to Iran "could be as beneficial to our efforts to contain a nuclear armed Iran as sanctions."
"If the Syrian regime is replaced with another form of government that doesn't tie its future to the Iranians, the world is a better place," he said.
Forces loyal to President Bashar Assad encircled Homs - a focal point of anti-regime protests - and began shelling the city ton February 4.
At least 150 are believed to have died in the onslaught, but with communications to the city cut a definitive death toll remains elusive.
"Savage shelling that does not differentiate between military or civilians targets," Syria-based activist Mustafa Osso told The Associated Press.
He added anti-regime protesters had vowed to "fight to the last man" in the neighborhood of Baba Amr.
Many Syrians are calling Baba Amr "Syria's Misrata," a reference to the Libyan city where rebels fought off a brutal government siege for weeks, managed to hold the city and went on to play a key role in overthrow of Muammar Qaddafi.
Human rights activists reported Monday's shelling of Baba Amr killed five civilians, while 18 civilians were killed on Sunday.
Clashes between military rebels and Syrian forces are growing more frequent and the defectors have managed to take control of small pieces of territory in the north, as well as parts of Homs province.
Opposition leaders believe Assad is trying to subdue Homs - an important stronghold for anti-Assad groups - before a planned referendum Sunday on a new constitution.
The referendum would allow a bigger role for political opposition to challenge Assad's Baath Party, which has controlled Syria since a 1963 coup.
But the leaders of the 11-month-old uprising against Assad have dismissed the referendum as an attempt at superficial reforms that do nothing to crack the regime's hold on power.
Assad still counts on support from Iran and allies such as Russia, which fears losing its main Arab partner. But his government is facing escalating pressure and isolation from Western and Arab states.
The last UN death toll in January said 5,400 civilians had been killed in 2011 alone, but hundreds have been killed since then and UN officials formally stopped counting due to the chaos gripping the country.
The group Local Coordination Committees says more than 7,300 have been killed since March of last year, but no independent verification is available.