Sebastian Coe has threatened Russia with the "ultimate sanction" of expulsion from the International Association of Athletics Federations (IAAF) because of its refusal to admit it ran a state-sponsored doping programme.

The Russian Athletics Federation (RusAF) was suspended in November 2015 after the publication of a World Anti-Doping Agency-funded report into allegations of endemic doping.

Only Russian athletes able to prove they have been tested by credible anti-doping agencies have been allowed to compete internationally since then, and only as neutrals. This meant Russia sent just one athlete to the 2016 Olympics in Rio and eight to the 2017 World Athletics Championships in London.

Several more have been cleared to compete since then but that avenue may now be closed because of RusAF's refusal to comply with the reinstatement criteria agreed with the IAAF in 2015.

That process is being overseen by a task force led by former WADA director Rune Andersen and his latest report was given to the IAAF Council on Tuesday in Birmingham, where athletics' World Indoor Championships were staged over the weekend.

He told IAAF president Lord Coe and his senior team that while progress was being made it has stalled and the key admission from Russia that its cheating was institutional seems no closer.

This is despite a second WADA-funded commission, led by Canadian professor Richard McLaren, and an International Olympic Committee investigation, led by former Swiss president Samuel Schmid, finding evidence that Russia systematically doped hundreds of athletes, across dozens of sports, for at least five years.

At a press conference in Birmingham, Andersen said without this acknowledgement the IAAF could have "no comfort it will not be repeated".

He pointed out that Russia's national anti-doping agency was still suspended by WADA and said he would be calling an "urgent meeting" with the Russian sports ministry to resolve the matter.

If that is not possible, Andersen said "we shall have to impose further steps".

Asked how he hoped to persuade the Russians to admit their cheating was directed by the state, he admitted "it's very difficult" but said "we can't move on, it's impossible" without the Russians accepting the findings of the McLaren and Schmid reports.

Coe said expelling RusAF would be a matter for the IAAF Congress, with its next meeting not scheduled until 2019.

"But we can't just sit here for ever and a day - it's costly and time consuming," the former London 2012 chief said.

"Unless dramatic progress is made we will have to review the status of the neutral competitors and ask congress to consider the ultimate sanction. It's not sitting there as a threat, we want it resolved. We want them back but there's no ambiguity in the criteria."

The Russian crisis was not the only matter addressed at what Coe described as the "most momentous" council meeting in the IAAF's history.

The federation also decided to reinstate a revised version of its hyperandrogenism rules.

Suspended by the Court of Arbitration for Sport in 2015, the rules were introduced in 2009 as a response to concerns about female athletes with naturally high levels of the male sex hormone testosterone, such as South African middle-distance star Caster Semenya, having an unfair competitive advantage.

As a result, female runners competing between 400 metres and a mile will be subject to a maximum level of testosterone. Any over the limit must medically reduce it.

The IAAF is confident this amendment will stand up to legal challenge but says the rules will be a "living document" that can be revised. They will come into force on November 1.

The council also debated plans to tighten up the rules around transfers of allegiance.