The family of Martin Finucane said it was "left in the dark" as to why he was targeted in a failed bomb attack at his west Belfast home.
Police said the device was thrown at a window at around 6.30am on Thursday and it did not ignite. They said it was fortunate the two adults - Mr Finucane and his son - in the property at the time were not injured and detectives are working to establish a motive.
A window was smashed and a vehicle heard leaving the area around the time. The device was later found in the front garden of the property.
Mr Finucane said he was not a member of any political party. He said he was woken by the sound of something hitting the window. He thought it may have been a snowball.
He described the device as having an accelerate, batteries and nails and was found on the window sill of the house. There was also a flammable cloth and gas cylinders found.
"It could have ignited.. thankfully it didn't," he said.
He called on those behind the attack to explain their actions.
"We all know threats have been issued to members Sinn Fein and their families. I would like them to explain why this has happened to me. I am not a member of Sinn Fein .. there is no justification for this."
The bomb squad attended to make the device safe.
Martin Finucane is the brother of murdered solicitor Pat.
Sinn Fein North Belfast MP John Finucane said the family were left in the dark as to why they were targeted. He branded those behind the incident "cowards".
"It's obviously something you should not have to deal with, but thankfully it's not as bad as it could have been if the device had ignited, or got into the house," Martin Finucane's nephew said.
"He's okay in the circumstances. He was in the house with his son, so obviously he's looking at a situation whereby it could have been serious damage to house, and also to himself and his son.
"There's a sense of confusion as well. There's no understanding at all as to why my uncle's house was targeted.
"He's made very clear that the people who carried out the attack should make sure that it is the last house that is attacked. That's there's no support for it, there's no room for that in this society."
The Finucane family are preparing to meet the Secretary of State on Friday to discuss a Supreme Court decision on upholding a decision by the government not to hold a public inquiry into the solicitor's 1989 killing. It will be their first meeting since the ruling, which found an effective investigation into the murder was not carried out.
"That's what our efforts have been focused on this week and to have this to deal with as well, is not something our family - or any family - should have to deal with," John Finucane continued.
"Police were at the scene carrying out their investigation but there's no understanding at this stage at who is behind it.
"We're still in the dark and we're still reacting to what happened a few hours ago.
"(My uncle) will deal with it and he'll get all the support he needs.
"It was a device that had an accelerant, batteries and nails and if had of penetrated the window and got into the house, this could have been a very different situation.
"It's very cowardly. It shouldn't happen. I would ask them to rethink what it is they were out doing this morning. To attack my uncle is something that shouldn't happen. I would call on people with influence to make sure that that is the last time someone's home is attacked."
Martin has traveled the world to shine light on state collusion, in his brother's case and hundreds of others. Our solidarity is with himRelatives for justice
Mr Finucane is a founding member of the victim campaign group Relatives for Justice.
It said it was "sickened" to learn of the bomb attack.
"Martin has traveled the world to shine light on state collusion, in his brother's case and hundreds of others. Our solidarity is with him this morning," the group said.
The Pat Finucane Centre, a campaign and advocacy organisation, said it was "shocked" at the attack on one of its board members.
The attack has been widely condemned.
Sinn Fein MP Paul Maskey described it as "wreckless".
"And shows a callous disregard for the Finucane family and the local community," he said.
“This is an attack on a justice and human rights campaigner and as such is an attack on the whole community.
“Those behind this device have nothing to offer society. I would call on anyone with any information on those responsible for this attack on a home to bring it forward to the police.”
I stand with Martin Finucane and his family. An attack on a human rights campaigner is an attack on us all. I have no words for those who are responsible.— Cllr Daniel baker (@danielbakersf) February 20, 2020
Pat Finuance, a high-profile solicitor, was shot dead by loyalist paramilitaries. There has been long-standing allegations that members of the UK security forces colluded in his murder.
He was shot in front of his wife and three children at their family home in north Belfast on February 12 1989.
The Finucane family has been campaigning for a full public inquiry into the brutal murder.
John Finucane, who is also a solicitor, was elected last December as MP for North Belfast.
He defeated former DUP MP Nigel Dodds.
Sinn Fein Lord Mayor of Belfast Daniel Baker - who replaced John Finucane as the city's first citizen - also condemned the attack.
"An attack on a human rights campaigner is an attack on us all. I have no words for those who are responsible," he tweeted.
SDLP West Belfast representative Paul Doherty said the attack showed a reckless disregard for both the Finucane family and the wider community.
“Those responsible have nothing to offer this community. We are trying to build a better west Belfast and acts like this only make that harder. They have to be faced down,” he said.
“I would appeal to anyone with information to bring it forward and offer my thoughts to Martin and the wider Finucane family.”
Police are appealing for information.
Detective Sergeant Keith Wilson said: “A motive for this attack has not yet been established. We are extremely fortunate no one was injured in what was a reckless act in a built up area.
“I am appealing for anyone who was in the area of Glenties Drive around the time of the incident and who witnessed any unusual activity or vehicles to contact detectives in Musgrave Police Station on 101 quoting reference 212 20/02/20. Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime.”