The Syrian Observatory for Human Rights said US-led air strikes destroyed a bridge near the IS-held town of Albu Kamal in Deir Ezzor province early on Friday, the third key bridge in the area to be destroyed by coalition strikes in the past week.
"The strikes destroyed a bridge... Outside of the town of Albu Kamal, cutting the border town and the surrounding area off from the rest of Deir Ezzor," said Observatory director Rami Abdel Rahman.
Eastern Deir Ezzor province is almost entirely controlled by IS, with the exception of the provincial capital and its military airport, which are held by government forces.
The oil-rich province is a key part of IS's self-proclaimed "caliphate", and borders territory under its control in Iraq.
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The Observatory said coalition aircraft earlier this month dropped leaflets in parts of Deir Ezzor warning that it planned to target bridges and urging civilians to avoid them.
The strikes are intended to "paralyse IS inside of Deir Ezzor", Abdel Rahman said, adding that the group "uses these bridges for movement inside the province and from there to Iraq".
Asked about the destruction of bridges in Deir Ezzor, a US defence official confirmed that the coalition was working on "cutting IS lines of communications to further restrict its ability to move around the battlefield".
Today, Syrian state television quoted the foreign ministry as criticising the coalition for targeting infrastructure.
The US defence official acknowledged that destroying the bridges would affect civilians, but described Deir Ezzor as "an important crossroads" for IS.
"More harm will be done to the Syrian population if IS is allowed to continue to use these bridges," he said.