As violence rages close to the Syrian capital, a U.N. convoy heads to Douma.

Smoke rose from the city where international observers visited hospitals Tuesday.

Amateur video posted online Monday appeared to show an attack by government forces on the city.

Helicopters also participated in the onslaught for the third day, according to one activist.

Reuters cannot verify the content of the video.

A Syrian officer said he did not guarantee the safety of the observers in the area.

The full U.N. mission was suspended in mid-June over concerns for the safety of monitors, but limited humanitarian operations continue as world leaders struggle to resolve the crisis.

Lindsey Parietti, Reuters