The US Senate has failed to approve a much-heralded compromise bill designed to make it possible for millions of illegal immigrants to become citizens.
About 500,000 illegal immigrants are thought to arrive every year
Supporters of the bill were able to muster only 38 of the 60 votes they needed to protect it from amendments introduced by opponents of the deal.
Each party blamed the other for the collapse of the deal.
President George W Bush has been urging US lawmakers to revamp immigration law for the first time in decades.
On Thursday, top senators from both parties lined up to praise the compromise deal they had reached, predicting it would get wide support in a vote on Friday.
It was blocked on procedural matters on Friday morning, however, leading both Senate majority leader Bill Frist and minority leader Harry Reid to speak of "obstruction" and "stonewalling".
But Senator Dianne Feinstein of California defended her opposition to the compromise, saying it would create a "complicated scenario in terms of enforcement, and therefore run the risk that it cannot be carried out well".
Mr Frist said the Senate would have to delay fuller consideration of the bill.
The Senate is about to begin its two-week spring recess.
Length of stay
The compromise proposal blocked on Friday would have divided illegal immigrants into three categories based on how long they had been in the US:
- Those who arrived five years ago or more to be allowed to stay subject to various criteria, including a criminal background check
- Those who have lived in the US for two to five years would be able to get a temporary work visa - after first leaving the country and being fingerprinted and processed on their return. They would have priority in applying for US residency over future immigrants entering as temporary workers
- Those who have been in the country for less than two years would be required to return to their countries of origin
The issue has shattered traditional political alliances, and brought hundreds of thousands of demonstrators - many of them Hispanic - onto the streets of Los Angeles, Chicago and other US cities.
More demonstrations are planned for Monday.
More than 11 million illegal immigrants are estimated to live in the United States.