The family members of a 9/11 survivors group have expressed gratitude to US President Joe Biden for eliminating al-Qaeda chief Ayman al-Zawahiri in a CIA drone strike in Afghanistan, saying it was a "significant step" in their years-long battle for justice and accountability.

The 9/11 Justice, a grassroots organisation comprising survivors, first responders, and family members who lost their loved ones in the September 11, 2001 terror attacks in the US, expressing joy over the terror group leader's death, said the step was particularly meaningful to the 9/11 community who continued their battle for justice.

The group, in a statement, further urged Biden to continue to stand with the 9/11 community and support all those who seek justice for victims of the 9/11 attacks that left 2,977 people dead.

Terry Strada, national chair of 9/11 Families United, expressed her gratitude for the commitment of intelligence agencies and the unflinching dedication shown by the US military in the fight against terrorism.

"If we're going to be serious about accountability, we must hold everyone accountable," Strada was quoted as saying by Fox News.

Brad Blakeman, a senior advisor to former president George W. Bush, whose nephew, a first responder, was killed in the attack, said: "It was a long day in coming. It should have been done a long time ago if we had the opportunity."

"What really dismays me is the fact that why is the US always the one to take action against the terrorists when they're harboured in sovereign countries like Afghanistan and Pakistan in the case of (Osama) bin Laden?

 Why are these countries giving safe haven to these murderers and terrorists," Blakeman said, expressing outrage at countries like Afghanistan and Pakistan for serving as a safe haven for such groups.