The US Senate has cleared the way for approval of $US1.1 billion ($A1.51 billion) in immediate funds to battle the Zika virus that is linked to birth defects, well above what is in legislation pending in the House of Representatives.
By a vote of 68-29, senators limited debate on the measure, paving the way for likely Senate approval this week.
Two other funding approaches failed to get enough support to advance in the Senate.
Meanwhile, the White House threatened to veto a $US622.1 million Zika bill poised to pass the House of Representatives later this week, saying it was "woefully inadequate".
Unlike the Senate legislation, the House bill also requires that the $US622.1 million be fully offset with spending cuts elsewhere.
Many conservative Republicans in the House refuse to approve Zika funds that would add to federal budget deficits, while Democrats and some Senate Republicans favour treating the problem as an emergency that would not have to be financed with spending cuts.
It was unclear how long it might take the Senate and House to work out their differences once they pass their respective bills.
US health officials have concluded that Zika infections in pregnant women can cause microcephaly, a birth defect marked by small head size that can lead to severe developmental problems in babies.
The World Health Organization has said there is strong scientific consensus that Zika can also cause Guillain-Barre, a rare neurological syndrome that causes temporary paralysis in adults.
Last year, Brazil began detecting an increase in microcephaly and the virus has been spreading rapidly in the Americas, with new cases now being reported in warm climates in southern US states including Florida.
House Republicans argue their $US622.1 million bill, when coupled with $US589 million the Obama administration already shifted to Zika from unused funds to battle Ebola, would provide enough money through September 30, the end of this fiscal year.
The administration says it needs the emergency funds to help state and local governments eradicate mosquitoes that spread the virus and to develop a vaccine.
