A lot riding on Syria ceasefire deal, but little hope

U.S., Russia hammer out temporary truce deal ... 02:32

KILIS, Turkey -- The details of a temporary ceasefire secured by the U.S. and Russia in Syria. Secretary of State John Kerry said overnight in Germany that the pause in fighting would go into effect in a week.

The deal will allow food and humanitarian aid to reach Syrians starving in areas under siege by the regime of Syrian dictator Bashar Assad, much sooner, however -- as soon as Friday, a U.S. official told CBS News' Margaret Brennan.

U.S. trying to negotiate Syrian ceasefire 00:45

This is the first ceasefire agreed on by all the countries involved in the Syrian civil war. But CBS News correspondent Holly Williams, reporting from Kilis, Turkey, on the Syrian border, says its success is still doubtful, because the Russians say they'll continue their airstrikes against terrorist groups, which they've said in the past while also targeting America-backed rebels.

Syrian civilians are once again paying with their blood as the regime -- backed by the Russians -- claws back territory from rebel fighters. Russian airstrikes, which only started in September, seem to have tipped the balance in Syria's five-year-long civil war, giving the regime the upper hand.

This week, regime forces launched an assault on the town of Tel Rifaat, which had been a stronghold for the rebels, some of whom had been armed by the U.S.

Abdul Karim Bahloul, who ran a school in Tel Rifaat, told CBS News as he crossed the border into Turkey that the Russian and Syrian "shelling and airstrikes are random."

"Homes are destroyed, and children's bodies lie in shreds on the ground," Bahloul said.

Syrian regime forces, with help from their other vital ally, Iran, have also nearly encircled Aleppo, which was Syria's most populous city before the war began.

If the ceasefire plan doesn't succeed, 300,000 civilians could be completely cut off in Aleppo, as they were in the town of Madaya under a siege by the regime. More than 40 people there have starved to death.

Even if the ceasefire does take hold, it won't include extremist groups like ISIS and al-Nusra, so the bloodshed is unlikely to stop any time soon.

Tens of thousands of Syrians have fled the latest offensive, trying to cross the border to the safety of Turkey. But Turkey already has more than 2 million Syrian refugees and is reluctant to take any more.