Holdout rebels in Mali have refused to initial a peace deal agreed by other armed groups and the government, saying they could not accept the accord "in its current form".

The UN Security Council on Friday urged the main Tuareg rebel alliance, known as the Coordination for the Movements of Azawad (CMA), to initial the deal along with the other parties on Wednesday or face sanctions.

But the Coordination said in a statement overnight that it could not accept the accord without "amendments" that it had submitted.

These include demands such as the "official recognition of Azawad (the name used by Tuaregs for the northern part of the country) as a geographic, political and juridical entity".

The UN Security Council said the March 1 peace accord was a "historic opportunity" for Mali following the Islamist takeover in the north in 2012 that brought the country to the brink of collapse.

On Thursday, Malian Foreign Minister Abdoulaye Diop urged the council to put pressure on the Coordination to accept the accord and warned that a collapse of the peace effort would have "enormous risks" for Mali and the region.

The Malian government and a coalition of armed groups from the north known as the Platform have signed on to the accord, brokered by Algeria under UN auspices over the past eight months.

Wednesday's ceremony to initial the agreement was to be followed soon afterwards by a formal signing.

The Coordination "once more reiterates its wish that the amendments that it submitted to the international mission... be taken into account," the statement said.

A delegation of international and African diplomats who came to Kidal, the Coordination's northern stronghold, on March 17 rejected the demands, as did the Bamako government.

The accord negotiated under UN auspices provides for greater regional autonomy for the north in line with long-standing demands by Tuaregs and other groups.

Islamist militants seized control of northern Mali for more than nine months until a French-led military intervention in 2013 partly drove them from the region.

The council expressed concern over the security situation in Mali, where a UN peace force has suffered heavy losses during attacks by Islamist groups in the north.

At least 35 peacekeepers have been killed in action since the United Nations' MINUSMA force was deployed in July 2013, and 137 wounded in attacks.