Fighters of the Syria Democratic Forces (SDF) stand inside a building near Manbij, June 17, 2016.

US-backed forces now control 40 percent of the ISIS held Syrian city of Manbij after new advances in the last day that secured them key areas inside the strategic city near the Turkish border, a monitor said on Sunday.

The British-based Syrian Observatory for Human Rights said the Syria Democratic Forces (SDF), with the support of air strikes, had seized several much of the eastern part of the besieged city after slower advances in recent weeks mainly in the western sector.

The US-backed alliance includes a Kurdish militia and Arab allies that joined it last year.

It launched the campaign nearly two months ago with the backing of US special forces to drive ISIS from its last stretch of the Syrian-Turkish frontier.

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