ISLAMABAD (Reuters) - Islamic State leader Abu Bakr al-Baghdadi was killed on Saturday in a secret operation approved by US President Donald Trump and carried out by helicopters in northwestern Syria, the Pentagon official said, according to a Pentagon official.

Ahead of the news, the US president chirped on Twitter, saying "something very big has just happened," without elaborating.

But the White House said in a brief statement that Trump would make a "very important" statement on Sunday morning Washington time (13:00 GMT).

Trump is under pressure over a Democrat-led accountability investigation and is under fire for his decision to withdraw US troops from Syria.

Baghdadi, a 48-year-old Iraqi whose real name is Ibrahim al-Samarrai, broke away from al-Qaeda in 2013, two years after al-Qaeda leader Osama bin Laden was killed.

The State Department has offered a $ 25 million reward for information leading to his arrest.

Al-Baghdadi appeared publicly when he rose to the pulpit of the Grand Mosque of Nuri in Mosul in 2014 to declare the establishment of a “caliphate state”. He also appeared again about a year ago talking to some of the organization's leaders.