The United States Tuesday welcomed the decision by Syria's rebel Opposition National Coalition to take part in mooted Geneva peace talks.

"This is a significant step forward in the process to convene the Geneva conference, the goal of which is... establishing by mutual consent of the two negotiating delegations a transitional governing body exercising full executive powers," said State Department spokeswoman Jen Psaki.

"We also welcome the inclusion of representatives of the Kurdish National Coalition within the Syrian Coalition, ensuring the Coalition is more inclusive of Syria's diversity," she stressed.

Syria's main opposition grouping said Monday it will attend peace talks but only on the condition that President Bashar al-Assad transfers power and is excluded from any transition process.

In a statement issued after two days of meetings in Istanbul, the key National Coalition said it would take part in mooted peace talks in Geneva "on the basis of the full transfer of power."

It also stipulated "that Bashar al-Assad and those with the blood of Syrians on their hands have no role in the transitional phase and Syria's future.

However the Syrian government, while expressing willingness to attend the proposed Geneva conference, insists that Assad's departure from power is not up for discussion.

Psaki noted that "the Coalition cited the need for progress on humanitarian issues ahead of a Geneva II meeting, "notably permitting humanitarian access to besieged areas and the release of female and child prisoners."

She went on to say that the US will work closely with its international partners, including Russia, "to make progress on these humanitarian issues".

The Syrian opposition Coalition announced a new government this week, after months of delays, facing challenges on the ground from Kurds seeking autonomy and Al-Qaeda groups that reject its authority.

The interim government is under pressure to quickly provide services to citizens living in large swathes of rebel-held territory, particularly in Syria's north.

Meanwhile, jihadist groups including the Al-Nusra Front and the Islamic State of Iraq and the Levant have been busy for months distributing food and even school supplies.

Groups like the Al-Nusra and ISIL do not recognise the authority of the Coalition, which is based in Turkey.

More than 120,000 people have been killed in Syria since the conflict erupted in March 2011, according to the Syrian Observatory for Human Rights.

Millions more have been displaced inside Syria or have fled abroad as Syrian rebels, have clashed with government forces.