PARIS - UN special envoy Lakhdar Brahimi will go to Syria this week to try to persuade Bashar Assad's government to call an immediate ceasefire in an 18-month-old conflict with rebels, UN Secretary General Ban Ki-moon said on Tuesday.

Efforts by Brahimi's predecessor, Kofi Annan, to engineer a ceasefire collapsed within days, with neither the Damascus government nor opposition forces willing to abide by conditions for an effective cessation of hostilities.

Brahimi is to meet Assad as fighting rages in Syria's biggest city Aleppo and government forces pursue offensives to dislodge rebels from provincial bastions elsewhere, causing increasing spillover into neighboring countries especially Turkey, prompting Ban to warn against the danger of escalation.

Ban said Brahimi aimed to curb the bloodshed and negotiate a deal to allow more humanitarian aid into Syria, where a civilian protest movement has evolved into an armed insurgency and one million people have been driven from their homes.

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