Ryan to focus on "maintaining party's majority" in Congress as presidential candidate battles controversies.

Paul Ryan, the US House of Representatives Speaker, has told Republican legislators that he will no longer "defend" or campaign with presidential candidate Donald Trump, focusing instead on maintaining his party's majority in Congress.

The country's top elected Republican official made the comments during a conference call with the politicians on Monday, a source familiar with the call told Reuters news agency.

The call was arranged to work out how to handle the fallout from a video that surfaced on Friday showing Trump making indecent comments about women in 2005, including his ability to grab them by the crotch with impunity because, as a celebrity, "you can do anything".

But Ryan, who has had an uneasy relationship with Trump from the start and has criticised him on numerous occasions, stopped short of rescinding his endorsement, according to a person who listened to the conference call.

Ryan "said he will not defend Trump or campaign with him for the next 30 days", the source on the call said.

Several people on the call also said Ryan explicitly told House members: "You all need to do what's best for you in your district."

"It really is unprecedented," said Al Jazeera's Patty Culhane, reporting from Washington, DC.

"The Republican Party used to tell members what to do, but this time Ryan flat out said, 'Do what is best for you.' This has not happened in modern American politics."

Trump hit back quickly via Twitter, saying Ryan should "not waste his time" opposing the Republicans' White House nominee.

But AshLee Strong, a Ryan spokesperson, said after the call that there was "no update in his position at this time" in terms of endorsing Trump.

Ryan will "spend the next month focused entirely on protecting our congressional majorities", Strong told AFP news agency in an email.

But the source on the call appeared to suggest Ryan had effectively conceded the election to Trump's Democratic rival Hillary Clinton, who is leading in national polls and in several key battleground states.

"He will spend his entire energy making sure that Hillary Clinton does not get a blank cheque with a Democrat-controlled Congress," the source said.

The source said Ryan appeared to give Republican legislators the green light to cut ties with Trump.

"You all need to do what's best for you in your district," Ryan said, according to the person on the call.

Many Republican Congress members are worried that Trump's campaign could ruin their chances of holding their majorities in the elections and inflict long-term damage on the party.

Nearly half of all 332 incumbent Republican senators, Congress members and governors have condemned Trump's remarks, and roughly one in 10 has called on him to drop out of the race.

But any attempt to replace Trump on the ballot this close to election day would face major legal and logistical hurdles.

A defiant Trump went on the offensive in the second presidential debate on Sunday, saying Clinton would go to jail if he were president and attacking her husband, Bill Clinton, for his treatment of women.

The debate, the second of three before the vote, was remarkable for the bitter nature of the exchanges between the two.

Ryan has criticised Trump on numerous occasions in the past