* Rebels say awaiting regional mediation effort
* France convenes Security Council meeting on CAR
* Rebels demand South African withdrawal (Adds details, background)
By John Irish and Paul Marin Ngoupana
PARIS/BANGUI, March 20 Rebels in the Central African Republic called off a truce on Wednesday, accusing the government of reneging on a January peace deal, but said they would give regional mediators a chance to settle the dispute before they resumed fighting.
The Seleka rebel group, which came close to taking the capital Bangui late last year, said a 72-hour deadline for the president to honour the terms of the deal had now passed.
"All options are being studied by our military command ... President (Francois) Bozize ... should draw the right conclusion and present his resignation," the movement's spokesman Eric Massi said by telephone in Paris.
The expiration of the deadline meant "the possible resumption of hostilities," he added. No one was immediately available to comment from CAR's government.
France's foreign ministry said earlier on Wednesday it had convened a meeting of the U.N. Security Council to discuss the fragile situation in its former colony.
The standoff is the latest in a series of rebel incursions, clashes and coups that have plagued the landlocked nation in the heart of Africa since its independence in 1960.
CAR remains among the least developed countries in the world despite rich deposits of gold, diamonds and uranium.
The spill-over of conflicts in neighbouring Chad, Sudan and Democratic Republic of Congo have undermined efforts to stabilise it.
Seleka - a loose umbrella group of insurgents - made its advance on the capital last year after accusing the government of failing to honour an even earlier peace agreement to give its fighters jobs and cash in exchange for laying down their arms.
Regional powers including Chad and South Africa sent in troops to bolster the government and helped negotiate the January settlement.
Seleka says the president had now failed to keep his promise to send remaining South African troops out of the country and to incorporate 2,000 rebels into the army.
CAR spokesman Massi said all options were on the table ahead of the expected arrival in coming days of Chad's President Idriss Deby and Congo Republic's President Denis Sassou Nguesso to broker talks in Bangui.
Paris increased the number of its troops in CAR to 600 in December to protect citizens working there, many of them in the key mining industry.
French nuclear energy group Areva mines the country's Bakouma uranium deposit.
The United States said on Sunday it was concerned about worsening security, urging all sides to implement the ceasefire deal. (Editing by Andrew Heavens and Daniel Flynn)