Late last year, as Isis fighters battled to expand their stronghold on Libya's coast, militants came within 70km of the country's sole remaining chemical-weapons site, unnerving Libyan and American officials who feared that potentially deadly chemicals could fall into extremist hands.
In May, when the fighters struck 1.5km from the lightly guarded desert facility, killing two security officers at a checkpoint, they decided it was time to act.
The encroachment by Isis (Islamic State) on an installation outside the remote oasis town of Waddan, where 500 tonnes of chemical-weapon precursor materials were stored, set off a hurried chain of events culminating in a disarmament operation involving the United States, European countries and the United Nations.
The international effort, which concluded last week when a Danish ship unloaded the materials at a German port for destruction, is one of the rare successes that Western nations can claim in Libya since dictator Muammar Gaddafi's ouster in 2011 pitched the North African country into lawlessness and civil war.
"We were worried about this very dangerous material," said Mohamed Taher Siyala, Foreign Minister of Libya's unity government. If Isis were to capture the chemicals, he said, "it would be dangerous not [just] for us but for the international community."The mission was also a sign of the risks posed by vulnerable chemicals, even if they have not been weaponised, in former dictatorships and failed states throughout the Middle East.
The rush by the United States and its European allies to help Libya remove chemicals stored at the Ruwagha site, which had been Gaddafi's chemical-weapons farm, was also an indication of the uneasiness of US President Barack Obama's Administration about whether the shaky unity Government would be able to secure materials that could be made into mustard gas.
"We placed a high degree of interest in moving these chemicals out of the country," said a senior US official. "We had been focused on it since we learned it was there."
The removal comes as US warplanes continue daily strikes on Libya's coastal city of Sirte, where a small group of Isis fighters has managed to hold off militia forces affiliated with the Western-backed government for months.
Recent progress to weaken Isis has not ended the prolonged political crisis that has spawned competing governments in Libya's east and west and pushed the country to the brink of civil war.
This week, a powerful eastern commander seized major oil ports, further inflaming tensions that have prevented the unity government - which the United States and its allies see as the sole path to stabilisation - from consolidating its power.
According to a second US official, links between the officials responsible for Ruwagha and the unity government were tenuous at best, adding to the sense of insecurity about the stockpile.
We placed a high degree of interest in moving these chemicals out of the country
"Not to suggest that there was friction . . . but they didn't have somebody that they would report to with clear distinction and chain of command," the official said.
The material at Ruwagha, which included phosphorus trichloride and 2-chloroethanol, was the final remnant of a once-formidable chemical-weapons programme built up by Gaddafi.
When Libya joined the Chemical Weapons Convention in 2004, the Gaddafi Government declared a host of material it held in its chemical arsenal, including a vast store of bulk sulfur mustard agent. After Gaddafi's ouster, the new government came across additional chemical weapons, mostly artillery and bombs filled with mustard gas, which were then reported to the Organisation for the Prohibition of Chemical Weapons (OPCW), a global watchdog. By early 2014, all remaining weapons had been destroyed.
While some precursor materials were destroyed in 2015, nearly 500 tons of dual-use, toxic industrial chemicals remained at Ruwagha.
There was also an environmental hazard: The materials were stored in containers so corroded that chemicals were leaking into the soil.
Officials from the Libyan office responsible for chemical weapons had hoped to destroy the precursors domestically, using sophisticated plasma technology, but that proved impossible as a wave of kidnappings, insurgent attacks and militia clashes surged across the country.
Ali Gebril, who has been Libya's representative to the OPCW since 2010, said officials' fears about the remaining material increased in December 2015, when Isis fighters attacked a checkpoint at a site named Kheshoom al-Khail, about 70km from Ruwagha.
While US and Libyan officials believed Isis did not know about the presence of the chemicals, they feared the site, which had also been used to store conventional weapons, might be targeted away. Already, Isis fighters were suspected of employing chemical weapons in Iraq and Syria; this week, US warplanes destroyed a chemical-weapons factory in northern Iraq.
Their concern grew sharply when a second checkpoint was attacked in May, just 1.5km from the facility. "We started really to think how to remove the chemicals from where they are, " Gebril said, or at least to move them from that vulnerable location.
In mid-July, the unity government renewed an earlier request to the OPCW, more urgently this time, for help in removing the material. But securing international support to transport the chemicals would not be simple.
Under international rules, moving chemical-weapon material across international boundaries would require authorisation from the United Nations. But officials worried that involving the world body might draw unwanted attention about the existence of the chemicals.
Libyan officials also had a template as they made their request - the international collaboration to remove Syria's chemicals weapons in 2014. "We told them it was an investment in world peace and security," Gebril said. "We got huge support."
Rebecca Hersman, a former Pentagon official overseeing chemical-weapons issues who is now at the Centre for Strategic and International Studies, said the Libya operation, like the one in Syria, showed that such transport operations to remove chemicals could be cost-effective and safe, "rather than importing people and capabilities into that dangerous environment" to destroy them at the site.
Many people believed we couldn't deliver and move the chemicals
In Washington, American officials received regular intelligence information and satellite imagery of the site. In mid-July, Libyan officials piled about 20 barrels - Canada had helped the government purchase new, safer containers - onto a small convoy of trucks and drove them across the desert to the coastal city of Misrata.
"Many people believed we couldn't deliver and move the chemicals," Gebril said.
At the same time, US and European officials were scrambling to coordinate a way to get the chemicals out of Libya. On July 22, the UN Security Council voted to adopt a British-drafted resolution authorising member countries to transport the material from Libya.
The White House decided it would not call attention to the unanimous vote until the materials had safely left Libya. "Everything we did we wanted to be just as low-profile as we possibly could," the second US official said.
In late August, the materials were loaded at the port of Misrata onto a Danish ship, which was accompanied across the Mediterranean by Danish and British naval ships. They were bound for the German city of Münster, where the chemicals will be destroyed in a commercial facility over six to nine months.