Last month  authority chief planner Andrew Smith confirmed he had written to the embassy asking about the status of the land, where a large fence surrounds a site where grass grows over mounds of dirt and unpacked bricks are piled. The Yarralumla block is in the diplomatic enclave and within view of Parliament House.

Russia was reported to be starting work in 2015, but last year, it revealed that the builder it had engaged to develop the site had gone broke.

Also in 2015, Iran was given a deadline of early 2015 to start construction at its prime Yarralumla block which had been sitting empty for about 20 years.

But around the corner from the Russian block, across from the sprawling United States mission, a block leased by the Iranian Embassy remains empty.

Although the Iranian mission had plans to develop the site this year, it has been stymied by the recent death of the architect it engaged to oversee a new building.

These are just two examples of an ongoing problem with leases on Canberra’s diplomatic estate, overseen by the National Capital Authority.

The “use it or lose policy”, introduced as part of an inquiry launched in 2012 into vacant embassy blocks, has forced many diplomatic missions to stop stalling on plans to develop their allocated land, or risk giving it up for other nations.

But while there is no more free land in Canberra's diplomatic areas, Mr Smith said there were still at least 12 parcels of land in Yarralumla, Deakin and O’Malley that are leased by foreign missions but remain undeveloped, although all the lessees had taken action to prove there were plans “in the pipeline”.

In the meantime, the authority has been told to expect “one or two countries” to seek permission to establish missions in Canberra annually over the next 20 years, while still managing the ongoing demand for expanded or relocated missions.

Other options, such as allowing existing embassies to subdivide their sites and hand back existing land, or to establish missions in commercial areas, have been successful, but many countries still, unsurprisingly, want large sites to build free-standing embassies or compounds.

Authority chief executive Sally Barnes said the authority had recently been in conversations with the ACT Government over the possible land swaps to solve the land shortage in diplomatic areas.

The authority owns the empty lakeside precinct next to the newly opened Henry Roland Park near the city - and land much coveted by the City Renewal Authority.

The ACT Government could exchange this commonwealth land for potential diplomatic sites elsewhere in the city.

“We're talking to the ACT Government about valuations and what might be possible, and what could we swap for what,” Ms Barnes said.

She added that the precedent for such a swap was the 1995 land exchange that involved the Kingston Foreshore and the Acton Peninsula, now the site of the National Museum of Australia.

Member for Canberra Gai Brodtmann instigated the embassy land inquiry through the National Capital and External Territories Committee, after the authority began looking into the possibility of using a greenfield site in Yarralumla for new embassy land.

She said it quickly became clear that this portfolio of properties had not been monitored over several decades, while embassies held onto their parcels of land and dawdled over development plans.

“Here's the NCA looking at alternative sites for diplomatic missions when they weren't even using up the land that we already had. It just seemed completely absurd,” she said.

“It became an issue, and we got greater transparency around the processes.”

She said the nature and requirements of diplomatic missions was also changing, and while the existing areas were more or less full, it was important to consider other options.

"The world's changing, and the thing is that a lot of these countries are cash-strapped and they either don't want the four-acre block or they can't afford it, and so they are looking at alternatives," she said.

Ms Barnes said dealing with these leases involved a different kind of diplomacy, one that took into account the competing priorities of foreign nations.

Pakistan, for example, had a prime block of land for almost 60 years before it was finally nudged into action by the “use it or lose it” policy, building a new embassy in 2016.

A new embassy building for the Pacific island nation of Samoa is another recent addition to the estate.

But blocks leased by the Bangladeshi and Vietnamese embassies remain empty, while the authority negotiates the differing size and position requirements of the respective missions.