Under the plan, the Syrian government will end combat missions in specified areas held by the opposition.

Russia and the US will establish a joint centre to combat so-called Islamic State and al-Nusra fighters.

The plan follows a day of talks between US Secretary of State John Kerry and his Russian counterpart, Sergei Lavrov.

The plan would need both the regime and opposition "to meet their obligations", Mr Kerry said. The opposition had indicated it was prepared to comply with the plan, he said, provided the Syrian government "shows it is serious".

Mr Lavrov said Russia had informed the Syrian government about the arrangements and the Syrian government was "ready to fulfil them".

"The cessation of hostilities requires access to all besieged and hard-to-reach areas, including Aleppo", Mr Kerry said, so that humanitarian access can be granted to besieged eastern parts of the city.

Seven days after the start of the cessation of hostilities, Mr Kerry added, Russia and the US would establish a "joint implementation group centre" to fight the Islamic State group and the al-Qaeda-allied Nusra fighters.

Mr Lavrov warned that some mistrust remained, and that "there are some people who would like today's arrangement to be undermined".

The United Nations envoy to Syria, Stefan de Mistura, welcomed the agreement and said the UN would exert all efforts to deliver humanitarian aid.

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