Syria's main opposition bloc complained that "elements in the U.S. Congress" are obstructing the Obama administration's efforts to step up support for the rebels, as regime forces on Friday intensified their offensive on opposition strongholds.
President Barack Obama recently said the U.S. is willing to send weapons to the opposition. Even so, Washington has been reluctant to arm the rebels battling President Bashar Assad's troops because radical Islamic groups, including some with al-Qaida links, have emerged as their most effective fighting force. Western countries have also been concerned over the lack of unified command among rebel groups.
The Western-backed Syrian National Coalition urged Congress to back arms deliveries to the rebels.
"The Syrian Coalition is deeply concerned by reports indicating that elements in the U.S. Congress are delaying the administration's efforts to increase its support to the Free Syrian Army" it said in a statement late Thursday.
The coalition will ensure "that arms will not reach extremist elements," it added.
Syria's main rebel units, known as the Free Syrian Army or FSA, regrouped in December under a unified rebel command called the Supreme Military Council, following promises of more military assistance once a central council was in place. The Western-backed council is headed by Gen. Salim Idriss, who defected from the Syrian army, and a 30-member group of senior officers. Idriss spent 35 years in the Syrian military and is seen as a secular-minded moderate.
Some FSA units still operate autonomously, however, often fighting alongside more effective groups on the battlefield, including the al-Qaida-affiliated Jabhat al-Nusra, which has led most successful battles for army bases, villages and towns in the north along the border with Turkey.
The group, known in English as The Nusra Front, has claimed responsibility for several car bombs and suicide attacks on military installations and government buildings, including in the capital Damascus, the seat of Assad's power.
More than 93,000 people have been killed in the Syrian conflict that erupted in March 2011 with largely peaceful protests against Assad's rule but escalated into a civil war in response to a brutal governmentcrackdown.
Over the past year, the conflict became increasingly sectarian, with mostly-Sunni rebels assisted by foreign fighters while Assad's forces are bolstered by fighters of the Lebanese Shiite group Hezbollah.
The regime in Damascus is also backed by Russia and Iran, and Moscow has continued to supply Assad with weapons throughout the crisis, saying it is fulfilling existing contracts.
The U.S., its European and Gulf allies have backed the opposition in the conflict, sending funds and non-lethal aid to the rebels.
In recent months, the rebels have gotten more powerful weaponry, including anti-tank missiles and surface-to-air missiles, likely from Qatar and Saudi Arabia.
But rebel commanders say they still need more sophisticated weapons to more effectively battle Assad forces' superior fire power, including heavy artillery and fighter jets.
"The urgency of delivering these arms cannot be overstated as the regime continues to intensify its attacks on opposition forces in Homs, Aleppo and elsewhere in Syria," the coalition said in a statement Thursday, quoting Najib Ghadbian, its envoy to the U.S.
The SNC said at least 4,000 people have been trapped for weeks in Homs, "with no access to medical care, food, or protection."
Homs, Syria's third largest city and the capital of the country's largest province that borders Lebanon and Iraq, has been at the heart of a government offensive to secure a strategic strip running from Damascus to the Mediterranean coast and Syria's seaports. The government controls most of the city, although rebels have managed to hold on to several enclaves in the center of Homs for more than a year.
The Britain-based Syrian Observatory for Human Rights said fighting raged on Friday there, with clashes concentrated in the two contested areas of Homs, Khaldiyeh and parts of the old city.
The Observatory, which relies on the network of informants inside Syria, also said that Assad's troops have been pounding villages outside Homs with artillery, including in the area that is home to Crac des Chevaliers, one of the world's best-preserved Crusader castles.
There was also fighting in Aleppo, Syria's largest city, the Observatory said, with several airstrikes on rebel positions.
For most of the past year, Aleppo has been carved up between areas under government and opposition control. The opposition forces launched an offensive in the north last summer, capturing whole neighborhoods inside Aleppo.
The Observatory said clashes were also heavy near Nairab military airport outside Aleppo — an army facility the rebels have been trying to take for months.