Updated 5:00 PM ET
BEIRUT - Syrian forces intensely shelled the opposition stronghold of Homs as President Bashar Assad's regime also escalated attacks on rebel bases elsewhere, with helicopter gunships strafing areas in the northwest, activists said. The violence comes amid the deaths Wednesday of a French photojournalist and a prominent American war correspondent working for a British newspaper. In all, 74 people were killed nationwide.
Weeks of withering barrages on the central city of Homs have failed to drive out opposition factions that include rebel soldiers who fled Assad's forces. Hundreds have died in the siege and the latest deaths further galvanized international pressure on Assad, who appears intent on widening his military crackdowns despite the risk of pushing Syria into full-scale civil war.
"This tragic incident is another example of the shameless brutality of the Assad regime," U.S. State Department spokeswoman Victoria Nuland said of the journalists killed.
The Obama administration Tuesday to international military assistance for Syria's rebels, with officials saying new tactics may have to be explored if Assad continues to defy pressure to halt a brutal crackdown on dissenters that has raged for 11 months and killed thousands.
The White House and State Department said they still hope for a political solution. But faced with the daily onslaught by the Assad regime against Syrian civilians, officials dropped the administration's previous strident opposition to arming anti-regime forces. It remained unclear, though, what, if any, role the U.S. might play in providing such aid.
France was outraged over the journalists killed.
"That's enough now, the regime must go," said French President Nicolas Sarkozy.
French spokeswoman Valerie Pecresse identified those killed as French photojournalist Remi Ochlik, 28, and American reporter Marie Colvin, who was working for Britain's Sunday Times.
France's Foreign Minister, Alain Juppe, said the attacks show the "increasingly intolerable repression" by Syrian forces. French Communication Minister Frederic Mitterrand said of the journalists killed: "It's abominable."
Syrian activists said at least two other Western journalists -- French reporter Edith Bouvier of Le Figaro and British photographer Paul Conroy of the Sunday Times -- were wounded in Wednesday's shelling, which claimed at least 13 lives.
Syria's stalwart ally and major arms supplier, Russia, remained behind Assad, but said the bloodshed adds urgency for a cease-fire to allow talks between his regime and opponents.
The Syrian military has intensified its attacks on Homs in the past few days, aiming to retake rebel-held neighborhoods that have become powerful symbols of resistance to Assad's rule. For the government in Damascus, Homs is a critical battleground to maintain its control of Syria's third-largest city and keep more rebel pockets from growing elsewhere.
In the northwestern province of Idlib, a main base of the rebel Free Syrian Army, the Britain-based Syrian Observatory for Human Rights claimed that Syrian military helicopters fitted with machine guns strafed the village of Ifis. Syrian combat helicopters are primarily Russian-made, though they also have a number of French choppers.
Another opposition group, the Local Coordination Committees, said troops conducted raids in the Damascus district of Mazzeh district and the suburb Jobar, where dozens of people were detained. In Jobar, the group said troops broke doors of homes and shops and set up checkpoints.
The group also said troops backed by tanks stormed the southern village of Hirak and conducted a wave of arrests.
A Homs-based activist, Omar Shaker, said the journalists were killed when several rockets hit a garden of a house used by activists and journalists in the besieged Homs neighborhood of Baba Amr, which has come under weeks of heavy bombardment by forces from Assad's regime. At least 13 people were killed in Wednesday's shelling, including the journalists, activists said.
The U.N. estimates that 5,400 people have been killed in repression by the Assad regime against a popular uprising that began 11 months ago. That figure was given in January and has not been updated. Syrian activists put the death toll at more than 7,300. Overall figures cannot be independently confirmed because Syria keeps tight control on the media.
On Wednesday, the U.N. said that Secretary-General Ban Ki-moon would dispatch Valerie Amos, the undersecretary-general for humanitarian affairs, to Syria to assess the situation. No date was set.
Twenty of the deaths reported Wednesday were in Homs, where resistance forces include breakaway soldiers. Homs has drawn comparisons to the Libyan city of Misrata, which withstood withering attacks last year by troops loyal to Muammar Qaddafi.
Shaker said tanks and artillery began intensely shelling at 6:30 a.m. and was continuing hours later. He said the apartment used by journalists was hit around 10 a.m.