WASHINGTON - US House Republicans are working on changes to their healthcare overhaul bill to provide more generous tax credits for older Americans and add a work requirement for the Medicaid program for the poor, House Speaker Paul Ryan said on Sunday.

Ryan said Republican leaders still planned to bring the healthcare bill to a vote on the House of Representatives floor on Thursday. Speaking on the "Fox News Sunday" television program, he added that leaders were working to address concerns that had been raised by rank-and-file Republicans to the legislation.

Republicans remain deeply divided over the healthcare overhaul, which is US President Donald Trump's first major legislative initiative. It aims to fulfill his campaign pledge to repeal and replace the Affordable Care Act, popularly known as Obamacare, the healthcare program of his Democratic predecessor, Barack Obama.

Democrats say the Republican plan could throw millions off health insurance and hurt the elderly, poor and working families while giving tax cuts to the rich.

"We think we should be offering even more assistance than the bill currently does" for lower-income people age 50 to 64, Ryan, the top Republican in Congress, said of the tax credits for health insurance that are proposed in the legislation.

Ryan also said Republicans were working on changes that would allow federal block grants to states for Medicaid and permit states to impose a work requirement for able-bodied Medicaid recipients.

Trump told reporters in a brief conversation aboard Air Force One that he had meetings about healthcare reform over the weekend in Florida and that the effort to sell the proposal was going well.

Trump has been wooing lawmakers to vote for the bill. He won the backing of a dozen conservative lawmakers on Friday after an Oval Office meeting in which the president endorsed a work requirement and block-grant option for Medicaid.

Block grants would give states a set amount of money to cover people on the Medicaid program and provide flexibility in spending decisions. But there is no guarantee funding will keep up with future demands.

While Ryan said he felt "very good" about the health bill's prospects in the House, a leading conservative lawmaker, Representative Mark Meadows, told the C-Span "Newsmakers" program that there were currently 40 Republican "no" votes in the House.

Republicans hold a majority in the chamber but cannot afford to have more than 21 defections for the measure to pass.

On Saturday, three Republican opponents of the bill including Meadows, senators Mike Lee of Utah and Ted Cruz of Texas, met at Trump's Mar-a-Lago estate in Florida "negotiating with the president's team, trying to fix this bill", Cruz told CBS' "Face the Nation".

Meadows, a North Carolina Republican, said the changes being considered for the Medicaid program would not go far enough if they left it up to states to decide whether to put in place a work requirement.