Thousands of civilians remain trapped amid what has been described by a UN spokesman as a "complete meltdown of humanity."
"This may be my last video. More than 50,000 civilians who rebelled against the dictator [Syrian President Bashar] al-Assad are threatened with field executions or are dying under bombing," Lina Shamy, an activist in eastern Aleppo, said in a video shared on Twitter.
Syrian regime forces have seized much of eastern Aleppo, which has been held by rebels for four years. In their final, bloody push to retake the city, there are multiple reports that pro-government forces have carried out mass executions.
CNN has not been able to independently verify the execution reports, and the Syrian government did not comment on the killings in state-run media.
Abdulkafi al-Hamdo, an activist and English teacher in east Aleppo, shared a Periscope video on Twitter on Tuesday, saying he had given up on the international community.
"Don't believe anymore in United Nations. Don't believe anymore in the international community. Don't think that they are not satisfied with what is going on," al-Hamdo said. "They are satisfied that we are being killed."
"Russia doesn't want us to go out alive. They want us dead. Assad is the same. Yesterday there were many celebrations on the other part of Aleppo. They were celebrating on our bodies," he added.
Salah Ashkar, another activist in Aleppo, made a final plea for people to protest in solidarity with Aleppo at the UN.
"Please, go to the embassies and block the way. Go to the UN headquarters and block the way. Please, don't let them sleep. Do it, do it, do it, do that now. There is no minute to spare. Please, please, stand with Aleppo," Ashkar said in a video shared on Twitter.
Dr. Salim Abu Al-Nasser, a dentist in east Aleppo, shared a similar sentiment.
"This could be my final appeal ... everybody that can send a message to his government, to his country ... ask him to stop the aggression, stop the killing, stop the war," Al-Nasser said in a video circulating on social media on Tuesday.
Bilal Abdul Kareem, a Syria-based journalist trapped in eastern Aleppo, shared a "final message" on Monday. Kareem, who reports for On The Ground News and has worked with CNN in the past
, condemned the Muslim community for failing to help the people of Aleppo.
"This might be close to, if not the last communication," Kareem said in a Twitter video. "I would like to say to the Muslim ummah [community] that is out there ... guys you dropped the ball on this one."
Activist Monther Etaky tweeted a message of thanks to all those who "stood for humanity" in supporting the plight of Aleppo: "I would like to thank all the humans whose stood for the humanity with our case, i will never forget you if we passed to the other life."
Bana Alabed, a young Syrian girl who has captured global attention with her tweets from Aleppo, has shared a number of dramatic goodbye messages in recent days. On Tuesday, she posted yet another -- this time with even more finality.
"My name is Bana, I'm 7 years old. I am talking to the world now live from East #Aleppo. This is my last moment to either live or die," Alabed wrote on Twitter.