Satellite images of Syria show that 83 percent of the country's lights have gone out over four years of devastating conflict that has left cities shattered and forced millions of people to flee their homes.

A global coalition of human rights and humanitarian groups released the analysis late Wednesday and demanded a comprehensive effort to get aid to Syrians still gripped by the crisis as it enters its fifth year.

Researcher Xi Li says a "staggering" 97 percent of the lights in the Syrian city of Aleppo have gone out since the conflict began. Aleppo has been destroyed by heavy fighting over the past two years between opposition fighters and government troops.

Li has measured the levels of nighttime light across Syria since the conflict began in March 2011.