DAMASCUS, Sept. 5 (Xinhua) -- The Islamic State (IS) suicide bombers are blowing themselves up as part of a counter offensive to close the breach the Syrian army has made into the years-long siege on Deir al-Zour city in eastern Syria, a monitor group reported on Tuesday.
Violent explosions and shelling flared on the outskirts of Deir al-Zour city by sunset Tuesday, as the IS militants launched a counter offensive to prevent the Syrian army from advancing into the city, said the Syrian Observatory for Human Rights.
This comes as the Syrian army and allied Iranian-backed fighters succeeded on Tuesday morning in lifting the three-year siege by IS on Deir al-Zour city with the help of the Russian air force.
The progressing forces broke the siege from the western part of the city through the Brigade 137, where a garrison of forces had been besieged by IS for three years.
The Syrian government hailed the achievement as a great victory against terrorism, with President Bashar al-Assad congratulating the soldiers there.
President Vladimir Putin also congratulated Assad on the victory, as Deir al-Zour is of a great strategic importance for the Syrian army.
The oil-rich city contains key gas and oil fields and it's also bordering Iraq.
Deir al-Zour is also the last stronghold for IS in Syria, with the Raqqa city, the de-facto capital of IS in northern Syria, is gradually falling to the U.S.-backed Syrian Democratic Forces (SDF), making the days of IS in Syria numbered if they lose Deir al-Zour.
In its report, the observatory said the IS counter offensive targeted the breach the Syrian army has made into the siege amid intense battles in the area.
The London-based watchdog group claimed that the passage opened by the Syrian army toward the Brigade 137 is exposed to the snipers of IS.
Meanwhile, other activists said that the U.S. has carried out two airdrops in Deir al-Zour over the past 24 hours, evacuating IS commanders out of the city, mainly the foreign fighters.
Syria and its allies have been accusing the U.S. of backing IS.
A statement issued earlier on Tuesday by the joint operation room of Syria's allies said the liberation of Deir al-Zour wouldn't have been delayed if it weren't for the U.S. and the coalition it's leading.
"The U.S. strike against Syrian military forces in Deir al-Zour helped Daesh expand in an attempt to control the entire city," the statement said, using the Arabic acronym for IS.
The U.S. intervention has complicated the situation in Syria and prevented the Syrian army from advancing on several fronts, it said.
Furthermore, the statement accused the U.S. of abetting IS, citing testimonies from captured IS militants about the U.S. involvement in transporting IS commanders from Deir al-Zour ahead of the entry of the Syrian army.