At least 20 Islamic State (IS) militants have been killed over the past 24 hours as a result of US-led airstrikes on the IS-held areas in eastern Syria, a war monitor group reported on Wednesday.The IS militants were killed as the US-led coalition has been pounding the IS-held areas in the eastern countryside of Deir al-Zour province as a prelude to a campaign to dislodge IS from its last strongholds in eastern Syria.The Syrian Observatory for Human Rights said the US-backed Syrian Democratic Forces (SDF), which is a Kurdish-led group, is bracing to launch a second wave of attacks against IS in the last IS-held pocket on the eastern bank of Euphrates River near Iraq.The airstrikes have recently intensified as the Kurdish-led group's attack on IS seems imminent after a failing attempt that has dragged on since September 10.In the process, civilian casualties have fallen, with tens of civilians reportedly killed earlier this week by the US-led strikes.The Syrian government has for long questioned the intentions of the US-led coalition as the area in the eastern countryside of Deir al-Zour is a strategic one due to its proximity to the Iraqi border and the oil-rich fields.Earlier on Wednesday, Syria's state news agency SANA said the US-led warplanes are targeting residential areas in eastern Deir al-Zour with cluster bombs and white phosphorus.The Syrian Foreign Ministry renewed in a statement Saturday calling on the UN to form "an independent international mechanism" to investigate into the "crimes of the Washington coalition" and punish the perpetrators.