Three families of Hillsborough disaster victims have made allegations of surveillance by undercover officers, the police watchdog has said.
In a monthly update, deputy chair of the Independent Police Complaints Commission (IPCC), Rachel Cerfontyne, said a letter from Broudie Jackson and Canter, the legal representatives of 22 families, had been received with specific allegations relating to one individual.
Another family alleges that a member of the family was placed under surveillance, Ms Cerfontyne said, while a third alleges they had property stolen from them.
The IPCC has also accepted an offer from the Home Secretary to write to all police forces and ask for disclosure of all documents on Hillsborough.
Scotland Yard refused to comment last month on claims undercover officers spied on Hillsborough campaigners.
It refused a Freedom of Information request by the magazine Private Eye for files on the Hillsborough Justice Campaign and the Hillsborough Family Support Group amid claims the campaigners were put under surveillance.
The force has a policy to neither confirm nor deny what police moles have been up to, in a bid to protect officers who work undercover.
Ms Cerfontyne said the Home Secretary's request may help in identifying whether any documents relating to surveillance exist.
Yvette Cooper MP, shadow home secretary, said the proposal was called for by Labour in Parliament.
"I am glad the Government and the IPCC has accepted more action is needed over the Hillsborough investigations," she said. " We called in Parliament for the Home Secretary to instruct all police forces to provide any information to the investigations and I welcome the Home Secretary's action."
She added: "The IPCC's announcement that allegations of surveillance will be looked at is also a step forward but they need to do more.
"I still believe it is extremely important that the families should be given the full truth in response to their concerns that they were put under surveillance simply because they were pursuing justice for their lost loved ones."
Steve Rotheram, Labour MP for Liverpool Walton and Hillsborough campaigner, said: " Following the Home Secretary's statement to the House of Commons which I requested earlier this month, I am delighted that both the Home Office and IPCC have reacted quickly to the points that both MPs and the shadow home secretary raised.
"It is vital that we continue to work together so that the families maintain trust and confidence in the process."
Elsewhere in its February update, the commission said there were 12 police officers still to be interviewed of the 243 identified by them.
Of the 243, 23 are deceased, 12 were deemed unfit to be interviewed and 12 had declined to be interviewed.
The IPCC said there were indications that some of those who had declined to be interviewed had reconsidered.
A new inquest into the deaths of 96 Liverpool supporters at Hillsborough stadium on April 15 1989 is set to start at the end of March.
The fresh inquest into the disaster was ordered when a panel of three High Court judges, headed by the Lord Chief Justice Lord Judge, quashed the accidental death verdicts.
A damning report laying bare a cover-up which attempted to shift the blame for the tragedy on to its victims was published last September.
A new police investigation as well as an inquiry by the Independent Police Complaints Commission (IPCC) are also being conducted.