Trump prepares for fight over Supreme Court nominee

US President Donald Trump is preparing to unveil his Supreme Court nominee, seeking to tilt the bench to conservatives on long divisive issues including abortion and gun control.

Trump's choice intends to fill a vacancy left by the sudden death of conservative justice Antonin Scalia in February 2016, which left the highest US court with four conservative and four liberal justices.

Trump said he would announce the "very big decision" on Tuesday at the White House and claimed the candidate he has chosen is "unbelievably highly respected".

However, Democratic Senator Jeff Merkley of Oregon has vowed to filibuster Trump's nominee which means the president will need to swing some Democratic votes in the Senate to secure his candidate.

The Republicans hold 52 seats but need 60 votes to confirm a nominee.

Abortion, gay marriage and gun control are just some of the controversial issues on which the Supreme Court is the final arbiter.

Its members are confirmed by the Senate and serve life terms.