BEIRUT (AP) — The Latest on the Syrian conflict (all times local):

1:20 p.m.

The commander of the Russian forces in Syria says Russian jets have carried out more than 2,600 airstrikes in the past two weeks to support the government's efforts to drive Islamic State militants from an eastern city.

President Bashar Assad's troops on Tuesday broke the nearly three-year militant blockade of parts of the city of Deir el-Zour, marking a significant advance against the extremists.

In comments carried by Russian news agencies on Wednesday, Col. Gen. Sergei Surovikin said Russian jets made nearly 1,500 flights from a Syrian base in the past two weeks.

Surovikin said the Russian airstrikes killed an estimated 1,200 militants and destroyed an unspecified number of armored vehicles, ammunition depots and artillery.

1:15 p.m.

U.N.-mandated investigators say they have solid evidence a Russian-built plane used by Syrian President Bashar Assad's air force conducted a sarin-gas attack in the spring that killed at least 83 civilians and sparked a retaliatory U.S. strike.

The latest report by the Commission of Inquiry on Syria also says U.S. forces failed to take "all feasible precautions" to protect civilians in attacking alleged terrorists in Aleppo in March, destroying part of a mosque complex.

The report offers some of the strongest evidence yet of allegations that Assad's forces conducted the April 4 attack on Khan Sheikhoun in rebel-held Idlib province.

The U.S. quickly launched a punitive strike on Shayrat air base, where the report says the Sukhoi-22 plane took off.

The report issued Wednesday covers a span from March to early July.

1 p.m.

Syrian activists say fierce fighting is underway between pro-government forces and Islamic State militants around a garrison in the eastern city of Deir el-Zour.

Wednesday's fighting came the day after Syrian troops backed by Russia and Iran breached a nearly three-year IS siege of parts of the city near the Iraqi border.

By nightfall, activists said the IS militants had counterattacked with multiple suicide assaults near where the Syrian troops had linked up with government forces inside the city. Heavy fighting was ongoing around the military base of the 137th Brigade on the outskirts of Deir el-Zour.

The breaching of the siege was a victory for President Bashar Assad, and could soon provide relief for tens of thousands of civilians besieged by the militants since early 2015.