A SCOTS competitor who survived the explosions in the Boston Marathon has described how she searched desperately for her two children in the aftermath of the carnage.

Lynn Burnet was 600 yards away from the finish line she had passed 30 minutes earlier when she heard a "boom, boom" as the bombs went off, killing three people and leaving more than 150 injured.

They detonated in an area filled with spectators opposite the finish line, blew people's limbs off and left pellets and nail-like fragments lodged in people's bodies.

Eight-year-old Martin Richard, from Boston, and restaurant manager Krystle Campbell, 29, have been named among the victims of Monday's attack, with 17 people remaining critically ill in hospital. Martin's mother, Denise, and six-year-old sister, Jane, were in hospital with "grievous injuries".

Ms Burnet, 39, from Nairn in the Highlands, told how she ran to grab children Caleb, eight, and Hope, five, and get them to the safety of her hotel amid the scenes of confusion and panic.

Ms Burnet said: "I heard this awful sound. It was boom, boom. People started to look panicked. I forgot I had run a marathon running to find them."

Ms Burnet, who spent two years training for the race, carried her daughter for a mile as they fled to safety.

"It was terrifying," she said. "I don't think at the time you react because at the time I had my children with me, and my main priority was to get them back safely."

Other Scots competitors described the unfolding scene as President Barack Obama condemned the bombings as a "terrorist act".

The FBI confirmed it was one line of inquiry, but said there were "no known additional threats" beyond the two bombs which went off. There was a security clampdown in Washington DC and New York.

US Homeland Security Secretary Janet Napolitano said there was no indication the blasts were part of a broader plot.

Mr Obama, who had chosen not to use the word terrorist in the aftermath of the attacks, said it was a "heinous and cowardly" act, adding: "Any time bombs are used to target innocent civilians it is an act of terrorism."

He said it was unclear whether it was the work of a "malevolent individual" or a wider group.

It is believed the devices were two pressure-cooker bombs packed with shards of metal, nails and ball bearings. The devices were similar to those deployed in Afghanistan, India, Nepal and Pakistan.

Around 20 Scots are listed as having taken part in the race, with more than 370 Britons registered.

Glasgow entrant Lesley Ann Ramsay, who was at her hotel nearby after finishing the race, believes she had a narrow escape. She added: "If we had met at the meeting point where we had originally planned we would have been very close but luckily I collected my bag just next to our hotel so met there instead," she said. "I was very lucky."

Christina Mackenzie from Stornoway was on her way back to her hotel after finishing the race when the blasts occurred.

She said: "To see the way people have targeted innocent people there is sickening. You're going from the best moment of your life to the worst."

Regular marathon runner Carol Boyd, a 49-year-old council worker from Ayr, was understood to have still been racing when the explosions occurred.

Her daughter Caitlin, 19, said she had an agonising 30-minute wait before hearing her mother was safe. "I had just come home from work and hadn't even seen the news. I got a call from a friend saying 'have you heard about the explosions'," she said.

"For about half an hour, 45 minutes nobody was picking up the phone. I honestly don't have any words for it. I was just sitting shaking. I didn't even know whether my mum was still alive. Then she texted me saying 'I'm okay, I love you, I'll be home soon'."

Former Edinburgh University student and competitor Rosie Allister, 33, said: "I'm stunned. It's so hard to take in."