A dramatic last-minute demand by Republican Senator Jeff Flake has prompted US President Donald Trump to order an FBI investigation into his Supreme Court nominee Brett Kavanaugh over sexual misconduct allegations.

With tempers flaring on both sides, the Republican-led Senate Judiciary Committee approved Mr Kavanaugh’s nomination and sent it to the full Senate over Democratic opposition, with Senator Flake providing the decisive vote.

But Senator Flake, a moderate Republican who is retiring from the Senate in January, cast his vote only after asking the panel to request that the Trump administration pursue an FBI probe of the explosive allegations against Mr Kavanaugh and delay a final Senate confirmation vote for up to a week to let the investigation run its course.

Mr Trump granted the request.

Senator Flake’s action came a day after the committee’s jarring and emotional hearing into the allegations against Mr Kavanaugh that gripped the country, with university professor Christine Blasey Ford accusing him of sexually assaulting her in 1982 when both were high schools students in Maryland.

Mr Kavanaugh denied the accusation.

In a statement issued by the White House, Mr Kavanaugh said he would cooperate with the FBI.

The prospect of a new investigation put the confirmation chances for Mr Kavanaugh, a conservative federal appeals court judge nominated for a lifetime job on the top US court, in further jeopardy in a Senate only narrowly controlled by Mr Trump’s fellow Republicans.

Democrats, who have opposed Mr Kavanaugh’s nomination from the outset, had called for an FBI probe, but Republicans and Mr Trump had opposed the move.

“I’ve ordered the FBI to conduct a supplemental investigation to update Judge Kavanaugh’s file. As the Senate has requested, this update must be limited in scope and completed in less than one week,” Mr Trump said in a statement.

Senator Flake said it is up to the FBI to determine what allegations are credible.

Two other women have accused Mr Kavanaugh of sexual misconduct, allegations he also denied.

If confirmed, Mr Kavanaugh would consolidate conservative control of the nation’s highest court and advance Mr Trump’s broad effort to shift the American judiciary to the right.

Even before Senator Flake’s announcement, it was unclear if Republicans had the votes to confirm Mr Kavanaugh on the Senate floor.

Republicans hold a slim Senate 51-49 majority, making the votes of two other so-far undecided Republican moderates crucial: Lisa Murkowski and Susan Collins.

Mr Trump said Ms Murkowski and Ms Collins must do what they think is right.

“I’m going to let the Senate handle that. They’ll make their decisions. And they’ve been doing a good job,” Mr Trump told reporters in the Oval Office when told about Senator Flake’s move.

The Republican president, however, indicated he was sticking with Mr Kavanaugh’s nomination, saying he has not thought “even a little bit” about replacing him.

Mr Trump said he found Dr Ford’s testimony “very compelling” and Mr Kavanaugh’s angry and defiant response “incredible”.

The controversy has unfolded just weeks ahead of the November 6 congressional elections in which Democrats are trying to seize control of Congress from the Republicans, against a backdrop of the #MeToo movement against sexual harassment and assault.

-AP