By Nadoun Coulibaly and Mathieu Bonkoungou

OUAGADOUGOU (Reuters) - The elite guards behind a coup in Burkina Faso defied an ultimatum on Tuesday to surrender to regular troops loyal to the government, leading to a stand-off in the capital as they awaited a mediation mission by regional leaders.

Loyalist forces marched into Ouagadougou overnight saying they would disarm the 1,200-strong presidential guard, whose putsch just weeks before an Oct. 11 poll threatens to derail a transition back to democracy after last year's overthrow of longtime leader Blaise Compaore.

But as a 10 a.m. deadline to surrender passed, coup leader General Gilbert Diendere stood firm, saying he would await West African regional leaders' mediation efforts.

"I'm not stalling for time. I'm within the time allotted to me," he told a news conference. "I am still the president of the National Democratic Council (junta)."

Coup leaders and loyalist officers negotiated throughout the morning, and army chief General Pingrenoma Zagre said he would give time to the mediation efforts.

"In certain circumstances, there must be discernment and common sense in order, as much as is possible, to avoid fighting," he told the news channel France 24.

After meetings in Abuja, the presidents of Senegal, Togo, Benin and Nigeria, along with officials from the United Nations and the West African regional bloc ECOWAS, were due in Ouagadougou early on Wednesday, the Burkina presidency's press office said.

Last year, mass street protests toppled Compaore as he attempted to force through changes to the constitution to extend his 27-year rule. In the process, Burkina Faso had become a beacon for democratic aspirations in Africa, where veteran rulers in countries from Rwanda to Congo Republic are seeking to scrap term limits.

"SIGNS OF HOPE"

Diendere, Compaore's former intelligence chief and right-hand man, said he had acted to prevent the disbandment of the presidential guard and to block a decision to prevent Compaore's allies standing in the election.

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Overnight, he freed Prime Minister Yacouba Isaac Zida, who had been held captive since soldiers stormed a cabinet meeting on Wednesday. Interim President Michel Kafando, who had been released earlier, took refuge on Monday night in the French ambassador's residence.

Nigerian President Muhammadu Buhari said there had been signs of hope during the day.

"I am delighted today that there are reports of some measures of understanding reached towards the resolution of the crisis," he said, without elaborating.

ECOWAS Commission President Kadre Desire Ouedraogo urged the presidential guard to disarm, and the army to refrain from using force.

In a statement, he also asked the African Union and others not to implement sanctions on Burkina, saying the coup leaders appeared willing to restore the interim government.

Burkina Faso, a former French colony, is an ally of the United States and France in their fight against Islamist militants in the region, and hosts some 200 French special forces.

Crowds came out on the streets of Ouagadougou early on Tuesday morning chanting their support for the army's attempt to force Diendere to surrender. But as the deadline approached, most of them disappeared.

Senegalese President Macky Sall, the current ECOWAS head, had announced a draft deal on Sunday that included an amnesty for the coup leaders.

But this was swiftly rejected by civil society and opposition politicians, who said they had not been consulted.

(Additional reporting by Joe Penney in Ouagadougou, Makini Brice in Dakar and Felix Onuah in Abuja; Writing by Matthew Mpoke Bigg and Joe Bavier; Editing by Kevin Liffey)