ALEPPO, Syria -- The Syrian army continues seizing parts of previously rebel-held territory in Aleppo, the sprawling city that was once Syria’s thriving economic hub but has been reduced to rubble by weeks of relentless bombing.

Backed by Russia’s military both in the air and on the ground, President Bashar Assad’s forces have hammered opposition-controlled neighborhoods into submission, warning that any rebels who refuse to leave peacefully will be “destroyed.”

The U.S., along with France and Britain, is leading a new call for a ceasefire in Aleppo to allow humanitarian aide in for the roughly 200,000 civilians thought to still be trapped in the shrinking rebel territory.

“The urgent need now is for an immediate ceasefire to allow the United Nations to get humanitarian assistance to people in eastern Aleppo,” said a joint statement that was also backed by Canada, Germany and Italy.

The White House issued a fresh warning, parallel to the call for a ceasefire, that the U.S. and its allies in Canada, France, Germany, Italy, and the United Kingdom were prepared to “consider additional restrictive measures against individuals and entities that act for or on behalf of the Syrian regime.‎”

Russia (and to a lesser degree, China) has blocked all attempts at a binding United Nations resolution aimed at ending the bloodshed in Aleppo by wielding it’s veto power as a permanent member of the Security Council. The most recent example of which came just two days ago.

While the U.S. and allied nations have already imposed a raft of unilateral sanctions on individuals accused of aiding in the Syrian onslaught, those measures have failed to have any impact on the ground, while the Syrian regime has been emboldened by increasing Russian military support over the course of the last year.

According to army commanders, Syrian army troops had wrested control by Wednesday of about three quarters of Aleppo’s central al-Shaar district.

They didn’t arrive in time to help one couple, who’s saddest moment was captured by photographer Yahya Alrejjo.

Alrejjo tells CBS News he came upon a man, who identified himself only as Abu Mohammed, pushing his ailing wife Sabah through the streets in a wheelchair, looking desperately for medical help.

Yahya Alrejjo

He couldn’t find any, and Alrejjo’s image of Mohammed in the depths of despair as his wife dies next to him conveys the helplessness of civilians caught up in the grinding civil war. The powerful images were distributed by Syrian opposition activists.

The bereaved man told Alrejjo he had no idea what had become of their seven children.

As CBS News correspondent Debora Patta reports, it’s been five years since the war divided Aleppo, splitting the rebel-held east from the government-controlled west -- and wrenching families apart in the process.

With the army’s advance, however, Mohammed Dokman got the chance on Tuesday to see his mother Zaliha for the first time in five years. They couldn’t contain their emotions.

“My soul,” sobbed the mother as another of her sons joined in the long-anticipated embrace, “you are everything to me, my son.”

Zaliha Dokman, right, hugs her son Mohammed as they are reunited for the first time in five years in part of Aleppo that has been retaken from rebels by Syrian army forces, Dec. 6, 2016. CBS

Zaliha remained in rebel-held Eastern Aleppo while her three sons and their families lived in the government-controlled west.

Her sons joined the Syrian army, and their uniforms marked them as enemies of the opposition, so visiting their mother in rebel-held territory became impossible.

Dokman knew the bombs unleashed on the opposition fighters by the army he served were raining down on his mother’s home, too.

“All the time I was helpless,” he told Patta. “I was constantly thinking I would lose her.”

In those five long years, much has changed. The neighbourhood Dokman and his brothers grew up in is unrecognizable.

But for a brief moment, the horrors of war were put aside; Zaliha gets to know the grandchildren she’s never met, and then it was finally time for them to go home, together.