Reports of a historic deal over immigration reform may be "premature", two of the senators tasked with forging cross-party consensus on the issue warned Sunday.

A bipartisan group of senators has been working for months on what would be the biggest shake-up of immigration policy since 1986. This weekend it was reported they had made a major breakthrough over the controversial issue of guest worker visas.

But on Sunday, Florida Republican senator Marco Rubio, a member of the so-called gang of eight senators leading the reform talks, said reports about a full agreement were "premature".

"We have made substantial progress and I believe we will be able to agree on a legislative proposal that modernizes our legal immigration system, improves border security and enforcement and allows those here illegally to earn the chance to one day apply for permanent residency," Rubio said in a statement. "However, that legislation will only be a starting point."

The push for reform is being led by a group of senators including veteran Republican John McCain and Democrat Charles Schumer.

Another Republican member, senator Lindsey Graham, told CNN's State of the Union that an outline of a deal on immigration had been agreed with business and labour leaders and will be rolled out next week.

"I think we've got a deal. We've got to write the legislation, but 2013, I hope, will be the year that we pass bipartisan immigration reform," Graham said.

"It will pass the House because it secures our borders, it controls who gets a job... [and] the 11 million [undocumented workers] will have a pathway to citizenship, but it will be earned, it will be long, and it will be hard," Graham said.

On Saturday reports emerged that Schumer had brokered a deal between Thomas Donohue, president of the US Chamber of Commerce, and Richard Trumka, head of the AFL-CIO over guest worker programme.

"This issue has always been the deal-breaker on immigration reform, but not this time," Schumer said in a statement Saturday. The number of new visas for low-skilled migrants would initially be capped at 20,000 but would be adjusted in line with the economy. A third of the visa would be reserved for small companies. Businesses will have to prove they first tried to hire American workers. But Schumer warned Sunday that senators had yet to sign off on legislative language.

Rubio, seen as a potential presidential candidate in 2016, said: "We will need a healthy public debate that includes committee hearings and the opportunity for other senators to improve our legislation with their own amendments. Eight senators from seven states have worked on this bill to serve as a starting point for discussion about fixing our broken immigration system. But arriving at a final product will require it to be properly submitted for the American people's consideration, through the other 92 senators from 43 states that weren't part of this initial drafting process. In order to succeed, this process cannot be rushed or done in secret."