The Senate will move forward with a key vote this week on a Republican health bill but it's not yet known whether the legislation will seek to replace President Barack Obama's health care law or simply repeal it.

Sen. John Thune of South Dakota, the third-ranking Republican, said Senate Majority Leader Mitch McConnell will make a decision soon on which bill to bring up for a vote, depending on ongoing discussions with GOP senators. Thune sought to cast this week's initial vote as important but mostly procedural, allowing senators to begin debate and propose amendments.

But he acknowledged that senators should be able to know beforehand what bill they will be considering.

"That's a judgment that Senator McConnell will make at some point this week before the vote," Thune said, expressing his own hope it will be a repeal-and-replace measure. "But no matter which camp you're in, you can't have a debate about either unless we get on the bill. So we need a 'yes' vote."

He said the procedural vote will be held "sometime this week."

President Donald Trump has said he wants Congress to repeal and replace Obamacare, but would accept a straight-repeal of the law if senators couldn't reach agreement. In a sign of the high stakes involved, Trump exhorted senators anew Sunday night to pass health legislation.

"If Republicans don't Repeal and Replace the disastrous ObamaCare, the repercussions will be far greater than any of them understand!" Trump tweeted.

The Republican-controlled House in May narrowly passed its version of a bill to repeal and replace the Affordable Care Act, or "Obamacare."

Senate Republicans are now considering two versions of similar legislation, one that would repeal and replace, and another that would simply repeal "Obamacare" with a two-year delay for implementation to give the Senate more time to agree on a replacement.

Both versions encountered opposition from enough GOP senators to doom the effort, but McConnell, R-Ky., is making a last-gasp attempt this week after Trump insisted that senators not leave town for the August recess without sending him some kind of health overhaul bill to sign.

In the Senate, Republicans hold a 52-48 majority. They can only afford to have one of their senators defect and still prevail on a health bill. That's because Republican Sen. John McCain is in Arizona dealing with brain cancer, while Democrats are standing united in opposition. Vice President Mike Pence would cast a tie-breaking vote.

Thune said no matter the outcome of the upcoming vote, senators would continue working to pass health legislation no matter how long it took, having promised voters they would do so.

"We are going to vote to repeal and replace Obamacare," he said, arguing that it was better if done sooner rather than later. "It's not a question of if, it's a question of when."

Still, at least two Republican senators Sunday appeared to reaffirm their intention to vote against the procedural motion if it involved the latest version of the GOP's repeal-and-replace bill.

Moderate Sen. Susan Collins of Maine said she continued to have concerns about reductions to Medicaid and criticized the Republican process, saying lawmakers were being unfairly kept in the dark. Under McConnell's plan, 22 million more people would become uninsured by 2026, many of them Medicaid recipients. She wants to hold public hearings and work with Democrats.

"We don't know whether we're going to be voting on the House bill, the first version of the Senate bill, the second version of the Senate bill, a new version of the Senate bill, or a 2015 bill that would have repealed the Affordable Care Act," Collins said. "I don't think that's a good approach to replacing legislation that affects millions of people."

Conservative Sen. Rand Paul of Kentucky said he would only support a repeal-only bill. That version would reduce government costs but lead to 32 million additional uninsured people over a decade. At least three senators including Collins have previously expressed opposition to that plan.

"The real question is what are we moving to? What are we opening debate to? Last week, Senate leadership said it would be a clean repeal ... and I think that's a good idea," Paul said. "The other alternative is the Senate leadership bill that doesn't repeal Obamacare, is Obamacare light and is loaded with pork. ... I'm not for that."

Thune appeared on "Fox News Sunday," Collins was on CBS' "Face the Nation," and Paul spoke on CNN's "State of the Union."