By David Morgan

WASHINGTON (Reuters) - Vice President Joe Biden on Thursday called on the Republican-led U.S. Congress to allow an up-or-down vote on funding to combat the Zika virus without other provisions attached, calling the health threat posed by the pathogen a national emergency.

Congress has failed to approve any funding to fight the mosquito-borne virus since President Barack Obama asked for $1.9 billion in February.

Lawmakers have been deadlocked for months over a $1.1 billion funding bill. Democrats have accused Republicans of attaching controversial provisions related to abortion that they cannot accept.

Republicans have accused Democrats of blocking the bill to gain political advantage by portraying Republicans as obstructionists on Zika funding.

"Give us an up-or-down vote, straight, on Zika," Biden said at an event on Capitol Hill with fellow Democrats from the Senate and House of Representatives.

"I understand attaching controversial issues to important legislation ... but this is a national emergency," Biden added. "People's health, the well-being of unborn children, the health of the country at large, is at stake. Act."

U.S. 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. There is no vaccine or treatment for Zika.

Two top federal health officials also visited Congress on Thursday to underscore the importance of Zika funding.

"We're all hopeful that the Congress will come through with the money that's needed to respond effectively to Zika," Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, told reporters after meeting with Senate Democratic leaders alongside Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

House Democratic leader Nancy Pelosi told reporters that Democrats want Zika funding added to stop-gap legislation that Congress must pass by Oct. 1 to keep federal agencies operating.

"By Zika, I mean for a year. I don't mean for three months," Pelosi said. "Zika should be emergency spending. It should not be off-set (requiring cuts in other government programs), because it is an emergency."

A main issue is Democrats' opposition to language, backed by Republicans, that they say would prevent Zika funds for abortion providers like Planned Parenthood, mainly in Puerto Rico.

The virus, first detected in Brazil last year, has spread rapidly through the Americas. Florida is the only U.S. state so far where local mosquitoes are known to be transmitting Zika.

(Reporting by David Morgan, Richard Cowan and Susan Heavey; Editing by Bernard Orr and Will Dunham)