On December 21, 1988, Pan Am Flight 103 exploded over the town in Dumfries and Galloway, 40 minutes into its flight from London to New York.
All 259 passengers and crew were killed, including 35 students from the University of Syracuse, along with 11 Lockerbie residents.
The crime scene covered 845 square miles, including rural Tundergarth.
Victims were of 21 different nationalities, and 190 were American.
Commemorations on Thursday will be “quiet, considered and low-key”, organisers said, with a remembrance service at Tundergarth Church and wreaths laid at Rosebank Crescent, which became the site of a huge crater, and Sherwood Crescent, where houses were also destroyed.
A remembrance scholar from Syracuse University will attend a rose-laying ceremony in Dryfesdale Cemetery with pupils from Lockerbie Academy, which has formed a scholarship programme with the US university.
A virtual service will also take place at Syracuse University.
Yousaf said the “strength and compassion victims’ families and the community of Lockerbie have shown” means they will never be forgotten.
“On the anniversary of the terrible events of December 21, 1988 in Lockerbie, my thoughts and sympathies remain with all those who lost loved ones on board Pan Am Flight 103 and those in the town of Lockerbie,” he said.
“My thoughts are also with the emergency workers who responded in the immediate aftermath of the atrocity. Their rapid response along with the people of Lockerbie while facing extraordinary circumstances demonstrated extreme kindness and humanity in the face of such horrific events.
“While those lost on that night can never be replaced, and the events have had a lasting impact on the town, I know links were forged following the disaster, including the Syracuse University scholarship programme with Lockerbie Academy.
“The strength and compassion that both the victims’ families and the community of Lockerbie have shown has created a legacy of friendship and ensured that the memory of those who died lives on.”
Organisers of the permanent memorial in Lockerbie said the impact of the bombing has been lifelong for survivors, and they are working to create a facility similar to the 9/11 museum in New York so the tragedy can be understood.
Lori Carnochan, 35, from the Tundergarth Kirks Trust, said some people who remember the Lockerbie bombing are still trying to get in touch with victims’ families to pass on messages about their loved ones.
Ms Carnochan said: “We speak about ‘our survivors’, the people who weren’t killed in Lockerbie.
“There’s people in Lockerbie who are only now speaking about it. There are people who were five, six, seven years old when it happened, who were still having nightmares or bed-wetting into their teens because of trauma they suffered that night.
“Lockerbie has a population of only 4,000 and a huge amount of people have PTSD (post-traumatic stress disorder). It’s such a small, close-knit community, lots of the victims were well known. Rural communities look after each other.
“Despite the terror which was rained down on them, people in Lockerbie were so welcoming to people from all over the world.
“Sherwood Crescent is where the huge crater was, houses were literally just vaporised. Rosebank Crescent is where houses were completely demolished and a huge amount of bodies found. At Tundergarth, around 100 bodies were found in the fields.
“These were people who were on the plane and the wind took them off in different directions when they landed. It is just horrific.”
A permanent exhibition in the Pan Am 103 Memorial Room in Tundergarth Church documents the lives of the victims and recognises “hometown heroes” who helped in the aftermath of the terror attack.
Ms Carnochan added: “It is still the deadliest terror attack in UK history, and the second deadliest in US history. It was the largest crime scene in UK history, with 845 square miles of debris.
“It is just unfathomable, the investigation has never closed.”
Former Libyan intelligence officer, Abdelbaset al-Megrahi is so far the only man convicted in relation to the bombing, after being found guilty of 270 counts of murder by a panel of three Scottish judges, sitting at a special court in the Hague in 2001.
He was sent to prison in Scotland, but was controversially granted compassionate release in 2009 after being diagnosed with terminal cancer, returning home to Libya where he died in 2012.
His family, and some relatives of the bombing victims, believe he suffered a miscarriage of justice but repeated appeals against his conviction have been rejected.
Fellow Libyan Abu Agila Mohammad Mas’ud Kheir Al-Marimi, 72, who is alleged to have helped make the bomb, faces three charges. He denied the charges when he appeared at a federal court in the US earlier this year.
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