He decided to study Arabic so he could read Islamic scriptures for himself and traveled to Sudan before settling in Egypt. There he got a job presenting an English-language religion program on a Saudi-funded television station, but he fell out with the channel’s management over his interest in current affairs and quit. He later made documentaries in Libya, Rwanda and elsewhere for an Islamic channel in Britain.

In 2012, he went to Syria to document how Islamist fighters who held territory were operating, and Syria has been his focus since. Early on, he collaborated with Western news outlets to produce reports about foreign fighters. But he felt that they only wanted “bad guy stories” that sensationalized the fighters, he said.

So he and some friends founded On The Ground News to produce original videos and articles from Syria that he distributes through Facebook, Twitter and YouTube. He said he received some funding from sympathetic individuals he declined to name.

Now 46, Mr. Abdul Kareem is married with five children, who live with their mother outside Syria. He declined to say where for fear that their association with him could cause them problems with the authorities.

Besides his family and being able to communicate with people in English, he misses “Italian pizza from New York,” he said.

He has covered different aspects of the war, including civilians wounded in airstrikes, the destruction caused by rocket attacks and the views of fighters, often near the front lines.

Running through his work is the view that the battle against the government of President Bashar al-Assad is a just Islamic cause against a brutal oppressor, and outrage that the world is not doing more to help out.