The EU embargo, imposed in May 2011 and expiring March 1, covers the Assad regime as well as the rebels.
Britain proposed renewing the embargo against the regime but removing it from the rebel forces, which would allow for delivery of lethal military equipment, diplomats in Brussels and in London told The Washington Post.
But during a meeting in Brussels Monday, most other EU governments opposed the idea, expressing fears more arms would lead to more bloodshed, the Post and British newspaper The Independent said.
"There is no shortage of arms in Syria," Luxembourger Foreign Affairs Minister Jean Asselborn said.
The EU governments instead agreed to renew the ban for three more months. They also promised to alter the embargo's terms to let more non-lethal equipment into Syria to save civilian lives.
"The U.K. believes international action so far has fallen short," the British Foreign Ministry said in a statement afterward. "In the absence of a diplomatic breakthrough, it is right that we continue to consider all options to protect civilians and to assist the [opposition Syrian] National Coalition and other opposition groups opposed to extremism."
A separate report issued Monday in Geneva by a U.N. commission said the umbrella Syrian National Coalition was getting dangerously involved with extremist Islamist fighters, drawn into the conflict because they see it as a Sunni jihad against President Bashar Assad's rule. This regime is technically secular but is dominated by Alawites, a branch of Shiite Islam.
The extremists joining the coalition include fighters from Libya, Tunisia, Saudi Arabia, Lebanon, Iraq and Egypt, the commission said.
The commission urged the coalition to separate itself from the extremist groups. This would make it easier for Europe, the United States and others to provide aid, it said.
After the vote in Brussels, some critics called the British defeat on arming the rebels an example of Western difficulty and even ambiguity in how to respond to the 2-year-old Syrian civil war, despite unanimous U.S. and European condemnation of Assad and his brutal means to stay in power, the Post and The Independent said.
The move -- opposed by Germany and Scandinavian countries as well as EU foreign policy chief Catherine Ashton -- was originally backed by France, The Independent said.
But Paris became lukewarm to it after troops it sent to northern Mali last month to help retake areas seized by Islamic militants found Western arms from Libyan rebels in the Muslim militants' arsenal, the newspaper said.
"Technical assistance and protection of civilians will be easier," French Foreign Minister Laurent Fabius said Monday.
Divisions within the Obama administration over what to do about the rising violence in Syria spilled into public view for the first time Feb. 7.
Defense Secretary Leon Panetta told the Senate Armed Services Committee on Capitol Hill he and Joint Chiefs of Staff Chairman Gen. Martin Dempsey supported a plan last year to arm carefully vetted Syrian rebels.
But they were ultimately overruled by the White House, he said, even though the plan was developed by David Petraeus, the CIA director at the time, and backed by Hillary Clinton, then the secretary of state.
The New York Times reported Tuesday White House officials could reopen the debate over providing weapons to select rebel members in the hope of breaking the impasse in Syria.
"This is not a closed decision," a senior administration official told the newspaper. "As the situation evolves, as our confidence increases, we might revisit it."