WASHINGTON — The Obama administration and its allies see few, if any, viable options to end the carnage in Syria as President Bashar Assad's forces continue their offensive against the opposition to his rule in what has become the uprising's most violent month.

With no appetite for a military intervention, a flagging Arab League initiative and the failed effort to win a U.N. Security Council resolution, officials said the current situation could continue for months. Plans for an international "Friends of Syria" conference and stepped-up humanitarian aid are seen as unlikely to change the grim calculus on the ground.

"What frustrates ... us is that there are no silver bullets here," said a senior administration official who spoke on the condition of anonymity. "There are no good options."

In the northern Syrian city of Aleppo on Friday, two suicide bombers struck compounds housing government security services, reportedly killing 28 people and wounding 238 in the worst violence to hit the country's relatively calm commercial capital since the uprising began in March. The government blamed the attacks on foreign-backed "terrorists."

Anti-Assad activists denied any involvement and accused the government of setting off the blasts to smear the opposition.

The bombings coincided with the military offensive against the central city of Homs, where activists claim hundreds of people have been killed in the past week in the sustained artillery bombardment of neighborhoods loyal to the opposition.

Satellite-image provider DigitalGlobe, based in Colorado, released photos Friday that it said show Syrian army tanks and other armored vehicles near apartment buildings in the city.

An opposition group said 16 people were killed Friday in Homs and 15 in the suburbs of Damascus.

The vetoes last weekend by Russia and China of the U.N. resolution condemning the crackdown and supporting an Arab League plan for Assad to surrender power appear to have emboldened the government to unleash even greater force to crush the uprising, which began as a peaceful revolt but is rapidly evolving into an armed insurgency.

Proposals from some quarters, including within the U.S. Congress, to arm the opposition Free Syrian Army, establish a no-fly zone over Syria or provide outside military protection for "safe zones" or a humanitarian corridor inside Syria are not under consideration, administration officials said.

On Friday, Turkish Foreign Minister Ahmet Davutoglu said Turkey is not providing arms or support to army defectors, whose ranks he estimated at 40,000, even though U.S. officials put the number much lower.

Davutoglu, in Washington, D.C., for consultations on Syria, said that the military's attacks against civilians "cannot be tolerated."

But he acknowledged, along with administration officials, that international intervention is not on the table. He called for rapid international action to supply humanitarian assistance to Syrian cities he said were in desperate need of food and other supplies.

The size and makeup of the self-described Free Syrian Army of defectors is unknown, it has no discernible command structure, officials said, and its ties with opposition political forces are tenuous. While the administration and others have looked to the Syrian National Council, an opposition umbrella, to consolidate different groups within and outside Syria, no foreign government has recognized it as the main opposition representative.

After the bombings Friday in Aleppo, the state news agency SANA said that two suicide bombers driving white minibuses struck within minutes of one another in separate neighborhoods about 9 a.m. The first attack targeted a law-enforcement department and killed 11 people, and the second struck a military security branch and killed 17, some of them children playing in a nearby park, the agency said.

Material from The Associated Press is included in this report.