A Polish couple who had gone to Manchester Arena to collect their daughters were among the victims.
Foreign Minister Witold Waszczykowski told a Polish radio station: “The parents came after the concert to collect their daughters and unfortunately we have information that they are dead. The children are safe.”
A spokesman for the country’s foreign ministry said “at least two people have died and one person has been injured” but could not confirm any further details.
Yesterday York University student Alex Klis said she was looking for her parents Angelika and Marcin, who had been missing since the attack.
In a post shared widely on Facebook she wrote: “Anyone who is in any safe place or hospital in Manchester, if anyone comes across my parents please please let me know as they’ve been missing ever since the attack.”
Meanwhile, the mother of a 15-year-old girl has paid tribute to her “precious” daughter, who was among the 22 people killed by suicide bomber Salman Abedi.
Olivia Campbell, from Bury, Greater Manchester, and eight-year-old Saffie Roussos and teenager Georgina Callander, were among the first of the terrorist’s victims to be named.
Olivia’s family had spent Tuesday frantically searching for her, but in the early hours of Wednesday Charlotte Campbell revealed her daughter had died in the blast.
Alongside a photo of Olivia she wrote on Facebook: “RIP my darling precious gorgeous girl Olivia Campbell taken far far too soon go sing with the angels and keep smiling mummy loves you so much.”
During her earlier emotional appeal, Ms Campbell said Olivia had been to the concert with her friend, Adam, who was receiving treatment in hospital.
“I last had contact with her at half past eight last night,” she told the BBC.
“She was at the concert, she’d just seen the support act and said she was having an amazing time and thanking me for letting her go.”
A further 59 people were injured when Abedi, 22, detonated a homemade device packed with nuts and bolts in the Arena’s foyer as thousands of young people left a concert by US pop star Ariana Grande.
Tributes have been paid to those killed in the blast, including Saffie, who was described by the headteacher at her school near Preston as a “beautiful little girl”.
Saffie had been at the concert with her mother, Lisa Roussos, and sister, Ashlee Bromwich, who is in her 20s, from Leyland, Lancashire.
They are both now in separate hospitals being treated for injuries, friends said.
Another victim was named by her college as Georgina Callander, who was studying health and social care at Runshaw College in Leyland, Lancashire.
The college spoke of its “enormous sadness” after hearing of Ms Callander’s death.
A spokesman said the teenager was on the second year of her course, and was a former student at Bishop Rawstorne Church of England Academy.
“Our deepest sympathies, thoughts and prayers go out to all of Georgina’s family, friends, and all of those affected by this loss,” the college said.
Tributes have also been paid to 26-year-old John Atkinson from Bury, who was named by friends on Facebook as a victim.
Friends of Mr Atkinson set up a fund for his family, which received more than £1,000 in less than an hour after being established.
“John was one in a million and loved by so many,” wrote Hayley Turk, who organised the fund through website GoFundMe.
“A true gentleman,” she added.
Kelly Brewster, from Sheffield, South Yorkshire, was reported to be among those missing following the attack.
Her partner Ian Winslow, later wrote on Facebook: “Not sure how this works but it isn’t good news. Kelly Brewster wasn’t one of the unidentified hospital patients. She has sadly passed away in the terror attack yesterday.
“Kelly really was the happiest she has ever been and we had so many things planned together. My daughter Phoebe will be absolutely devastated like we all are.”
Alison Howe, 45, from Royton, Greater Manchester, was reported missing by relatives along with her friend, Lisa Lees.
A family member wrote on Facebook late on Tuesday: “They took a caring beautiful mum and step mother away from us all she was amazing to us all x love you loads Alison Howe xx”