WASHINGTON -- President Obama said the U.S. would’ve had to be “all in and willing to take over Syria” for him to intervene more forcefully in the country’s civil war.

During his nationally televised year-end news conference Friday, the president said doing so wasn’t feasible for many reasons. It would’ve required many U.S. troops; he lacked support from Congress and the right under international law; the U.S. already had costly deployments in Iraq and Afghanistan; Syria’s opposition wasn’t prepared to govern; and Russia and Iran were protecting Syria’s government.

Mr. Obama said military options short of invasion were tempting because “we wanted to do something.” But it was “impossible to do this on the cheap.”

Mr. Obama said he asked himself if he could do something to save lives.

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But he said his No. 1 priority was doing what was right for America.

Aleppo, once Syria’s largest city but home to its rebel movement, has become a humanitarian crisis under Syrian government -- backed by Russia -- airstrikes. As CBS News’ Debora Patta reported earlier this week, the United Nations described the situation in the city as a “complete meltdown of humanity.”

Meanwhile, diplomats sought to salvage the evacuation of eastern Aleppo after it stalled amid recriminations by both sides in Syria’s civil war, raising fears the cease-fire could collapse with thousands still desperate to escape the rebel enclave.

The Aleppo evacuation was suspended after a report of shooting at a crossing point into the enclave. The Syrian government pulled out its buses that since Thursday had been ferrying out people from the ancient city that has suffered under intense bombardment, fierce battles and a prolonged siege.

“The carnage in Syria remains a gaping hole in the global conscience,” said U.N. Secretary-General Ban Ki-moon. “Aleppo is now a synonym for hell.”

The halt also appeared to be linked to a separate deal to remove thousands of people from the government-held Shiite villages of Foua and Kfarya that are under siege by the rebels. The Syrian government says those evacuations and the one in eastern Aleppo must be done simultaneously, but the rebels say there’s no connection.

The foreign minister of Turkey, a main backer of the rebels, said he was talking to his counterpart in Iran, a top ally of the Syrian government, to try to resume the evacuation.

A closed emergency meeting of the U.N. Security Council was held on the crisis in Aleppo, discussing a French proposal to have independent monitors oversee the evacuation of civilians and fighters. The council meeting ended with diplomats saying they would convene again this weekend.

The cease-fire and evacuation marked the end of the rebels’ most important stronghold in the five-year-old civil war. The suspension demonstrated the fragility of the cease-fire deal, in which civilians and fighters in the few remaining blocks of the rebel enclave were to be taken to opposition-held territory nearby.

In announcing the suspension, Syrian state TV said rebels were trying to smuggle out captives who had been seized in the enclave after ferocious battles with troops supporting President Bashar Assad.

Several opposition activists said Syrian troops shot and killed four people in one bus, but the incident could not be independently confirmed.

The Lebanon-based pan-Arab Al-Mayadeen TV broadcast images of the government buses apparently returning evacuees to eastern Aleppo after the road was closed.

Al-Manar TV, the media arm of the Lebanon-based Hezbollah militant group that supports Assad, said Syrian government supporters had closed the road used by evacuees from Aleppo, demanding the wounded from Foua and Kfarya be allowed to leave.

Syrian state media said rebels shelled a road that was supposed to be used by people leaving the villages. But the opposition’s Syrian Observatory for Human Rights said Hezbollah fighters backed by Assad ally Iran had cut the road to protest a lack of progress in the evacuations.

Buses that arrived at a collection point in the Hama countryside to pick up evacuees from the villages waited for hours to no avail.

Later, two rebel spokesmen privy to the talks said the fighters besieging the villages, including the al Qaeda linked Fatah al-Sham Front, had agreed to evacuate several hundred wounded from the villages.

Turkey’s state-run Anadolu Agency said Prime Minister Binali Yildirim had called Iranian Presidential Deputy Ishak Cihangiri and told him he was ready to cooperate with Tehran on the evacuation issue.

Reports differed on how many people remain in the Aleppo enclave, ranging from 15,000 to 40,000 civilians, along with an estimated 6,000 fighters.

There also were contradictory reports on the number of evacuees. Syrian state TV put it at more than 9,000; the Syrian state news agency said 8,079 opposition fighters and their families have left; and Russia, a key Assad ally, said over 9,500 people, including more than 4,500, were taken out.

More than 2,700 children have been evacuated in the past 24 hours, including the sick, wounded and those without their parents, UNICEF said. Hundreds of other vulnerable children, including orphans, remain trapped, it added.

“We are extremely concerned about their fate. If these children are not evacuated urgently, they could die,” UNICEF said in a statement.

There are still “high numbers of women and infants, children under 5, that need to get out,” added Elizabeth Hoff, Syrian representative for the World Health Organization, speaking by phone from western Aleppo.

During Thursday night’s evacuation, Pawel Krzysiek of the International Committee of the Red Cross told The Associated Press he could sense “fear, desperation (and) anxiety” among those waiting to escape.

The civilians - including children and the elderly, the wounded and the sick - were out in the cold, “burning the plastic, trying to get some sort of heat to warm themselves,” said Krzysiek, who is still in Aleppo.

“It’s the people leaving their house behind, their lives behind. It is very often they are facing impossible choices and this all occurs at the very individual level and it is difficult to compare with anything else,” he said.

“This is what the people are going through with their families, their relatives. This is really something very personal for them. I have seen sadness. I have seen really sadness in the people eyes. Heartbreaking sadness, broken lives, heartbreaking stories,” Krzysiek added.

Before the operation was suspended Friday, four convoys of ambulances and buses left Aleppo, Syrian state TV said, noting that some evacuees used their own vehicles.

Also on Friday, Syrian state media reported that a 7-year-old girl wearing a belt of explosives walked into a police station in the capital of Damascus, and her bomb was triggered by remote control, killing her and wounding a policeman.

In Japan, Russian President Vladimir Putin announced a new peace initiative, saying he and Turkish President Recep Tayyip Erdogan were working to set up talks between Damascus and the opposition. Putin said they would take place in Astana, the capital of the Central Asian country of Kazakhstan.

Bassma Kodmani of the High Negotiations Committee, Syria’s main opposition group, told the AP that her group supports the call for resumed peace talks but it wants them to take place under U.N. auspices and that it doesn’t believe Astana was “the appropriate place.”

Several rounds of U.N.-mediated indirect peace talks this year in Geneva were suspended with no progress.