Canadian Prime Minister Justin Trudeau spoke to Iranian President Hassan Rouhani over the phone after Tehran admitted to having “unintentionally” downed a Ukrainian airliner last week that killed all 176 people on board.

On Saturday, addressing the media, Trudeau said that Iran’s admission was an important step in providing answers for families, but more must be done.

“A full and complete investigation must be conducted,” Trudeau said.

“We need full clarity on how such a horrific tragedy could have occurred”, he added.

During their conversation, Rouhani promised a further investigation into the circumstances surrounding the plane crash.

Iranian President Hassan Rouhani said that the aircraft, which had flown close to a sensitive military site belonging to the elite Revolutionary Guards, was shot down “unintentionally due to human error”.

The Iranian military also put out a statement stating that the plane was mistaken for a “hostile target” after it turned toward a “sensitive military centre” of the Revolutionary Guard. It also blamed the “highest level of readiness” resulting from tensions with the United States.

On Saturday, Iran admitted to shooting down the Ukrainian plane that crashed early on Wednesday after taking off from the capital city of Tehran.

Iranian President Hassan Rouhani said that the aircraft, which had flown close to a sensitive military site belonging to the elite Revolutionary Guards, was shot down “unintentionally due to human error”.

The crash came hours after Iran launched a ballistic missile attack targeting two bases in Iraq housing US forces in retaliation to the killing of Revolutionary Guard Gen. Qassim Suleimani.

The United States and Canada had said that the plane was shot down.