Johnson said he believes Russia was involved in the bombing of an aid convoy near Aleppo.
Britain accuses Assad regime and Russia of committing war crimes by intentionally targeting hospitals.
Russian-backed offensive accused of using chemical weapons to take back rebel-held areas.
Government forces unleash fierce air assault with aim to capture all of Aleppo within a week.
Warplanes have mounted the heaviest air strikes in months against rebel-held districts in the city.
Weakened by years of food and medicine shortages, the people can't hold out.
The discovery is in contravention of Syria's promise to hand over its entire chemical stockpile for destruction.
Turkey is backing a Syrian rebel push across its border to remove the threat from the radical Islamist group.
Up to a million Syrian Christians have fled Syria, and the U.S. has accepted just 56. Why?
With the siege of Aleppo reinstated, Putin may have made Assad immune to a negotiated removal.
Newsweek speaks to "The White Helmets" filmmakers Orlando von Einsiedel and Joanna Natasegara.
Abu Hajer al Homsi was killed in a rural area of Aleppo province.
Activists and monitoring groups say many have been treated for breathing difficulties in rebel-held district.
Adnani urged jihadis to attack Western targets and masterminded the November 2015 Paris blasts.