The Obama administration and its allies see few, if any, viable options to end the carnage in Syria as President Bashar al-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.”

The bombings coincided with the ongoing 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.

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

Russia’s veto of the U.N. resolution last weekend condemning the crackdown — and supporting an Arab League plan for Assad to surrender power — appears to have emboldened the government to unleash even greater force in its effort 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, whose government has played a leading role in efforts to broaden the Syrian opposition to include minority groups, 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 for consultations on Syria, said that the military’s attacks against civilians “cannot be tolerated. We cannot wait and see [it become] like Sarajevo,” the Bosnian capital where Serbian forces rained artillery on civilians while the international community stood by and watched.

But Davutoglu acknowledged, along with administration officials, that international intervention is not currently 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. Administration officials said that aid was likely to consist of stepped-up supplies to non-governmental organizations operating in Syria.

The size and makeup of the self-described Free Syrian Army of defectors are unknown and 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.

Since Secretary of State Hillary Rodham Clinton met with leaders of the Council in Geneva in December, administration officials have been disappointed with the results of its efforts to reach out to minorities, including Christians and Shiite-related sects such as the Alawites, despite U.S. and European assistance. Minority failure to break with Assad is viewed as a reflection of fear, fanned by the government, of oppression under the Sunni-led opposition.

But in what administration officials now see as a vicious circle, increased regime violence against the opposition will promote exactly the kind of sectarian revenge the minority fears.

Those calling for a no-fly zone, administration officials said, misunderstand the nature of the violence in Syria — which so far does not include Syria’s air force — and underestimate the difficulty in mounting a complicated military operation that would include combat air patrols flown 24 hours a day, seven days a week. Syria also has a fairly sophisticated air defense system.

Protecting a humanitarian corridor would also require military forces that no government has been willing to provide and many believe would only worsen the situation. NATO has said it will not become involved in Syria, and a U.N. protection force would require Security Council approval.

A second administration official, who was not authorized to discuss military matters on the record, said that the U.S. “focus remains on applying diplomatic and economic pressure on the Syrian regime. Military planning occurs as a matter of course,” the official said. “As you would expect, some ideas are on the table” for Syria, “but nothing has been requested. It’s an academic exercise at this stage.”

For the moment, the continuation and expansion of the Arab League monitoring mission on the ground in Syria offers the only possibility to directly affect the violence, administration officials said. The mission was suspended last month amid fears for the safety of the monitors, and the Arabs have shown little inclination to send the monitors back without some kind of protection. The Arab League is meeting in Cairo on Sunday to discuss the situation.

On Friday, the U.S. ambassador to Syria, Robert Ford, posted on the Facebook page of the U.S. Embassy in Damascus satellite images showing what he said were Syrian troops firing mortar and artillery shells at residential neighborhoods in several cities.

Ford was recalled to Washington this week and the embassy was closed following a series of mysterious explosions in the capital in late December and early January in which at least 70 people died. The government blamed the attacks on al-Qaeda.

Following similar explosions in Aleppo on Friday, the state news agency SANA said that two suicide bombers driving white minibuses struck within minutes of one another in separate neighborhoods shortly after 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.

The residents of Aleppo, a mostly middle-class mercantile city, have largely refrained from taking part in the mass anti-government demonstrations that have swept much of the rest of the country.

But in recent weeks there have been signs that the unrest is reaching into the city, with protests erupting in several neighborhoods and suburbs as unhappiness grows with the levels of violence being used by the government to suppress its opponents elsewhere.

Free Syrian Army spokesman Col. Malik al-Kurdi denied that rebels had carried out the bombings, but he said they had staged attacks against Syrian security forces immediately beforehand.

“While our soldiers were withdrawing, the explosions took place,” he said. “We don’t know what really happened. It could be that their bombs and ammunition blew up or that they staged the explosions to imply that the Free Syrian Army has sophisticated explosives.”

Sly reported from Beirut.