OTTAWA -- The Liberal government will commit in Wednesday's federal budget to offer disabled veterans the option of a lifetime pension by the end of the year, The Canadian Press has learned.

While the actual details of the pension will be worked out in the coming months, the commitment to a specific timeline will mark an important benchmark for the Liberals' signature election promise to veterans.

Canada previously offered lifelong pensions to those hurt in the line of duty, but they were abolished in 2006 and replaced by a new system centred on a lump-sum payment for injuries and career training.

But the new system has become a lightning rod for veterans' anger, with many complaining that it provides less financial support over their lifetimes and demanding that the pensions be restored.

The Liberals were the only party to promise in the 2015 election to bring back life pensions for injured veterans, with the pledge serving as the centrepiece of their effort to court veteran voters.

In last year's budget, the government moved to increase the maximum lump-sum payment to $360,000 from $310,000, starting this April 1, with the increase retroactive for all who had received it.

They also topped up a number of financial benefits for veterans injured while in uniform and unable to work and re-opened nine Veterans Affairs Canada offices that had been closed by the Conservatives.

Those measures were expected to cost $5.6 billion over six years.

But many questioned whether the government would make good on its pledge to bring back the disability pensions, which both the Conservatives and NDP said would be prohibitively expensive.

Representatives from a number of veterans' groups interviewed earlier this week expressed frustration about the government's silence and perceived lack of progress on a number of fronts.

Those included providing free education to ex-soldiers and creating a new centre for veterans suffering from PTSD and other psychological injuries.

But the promise to bring back lifelong pensions as an option for disabled veterans alongside lump-sum payments and career training was clearly foremost in their thoughts.

"There's a lot of things left on (Veterans Affairs Minister Kent Hehr's) mandate letter that we're waiting for," said Deanna Fimrite, dominion secretary-treasurer of Army, Navy, Air Force Veterans in Canada.

"I think probably in the minds of most veterans it is: What is going to be done about lifelong pensions? I think that's number 1 on most of their lists."

Conservative veterans affairs critic John Brassard echoed that assessment, saying the pension is the top issue that ex-soldiers raise when he meets them.

The issue is also at the heart of a lawsuit filed in B.C., where six veterans from the war in Afghanistan have been fighting for years to either get the pensions reinstated or get equivalent compensation.

But while the commitment to deliver by the end of the year is expected to be welcomed, one of the next questions is what form the pensions will actually take.

Expectations are high for some veterans, who say only a full return to the old pension system will address their complaints about a lack of fairness and allay their anger.

But the reason the Liberals were the only party that promised to reintroduce the disability pensions was because of the expected costs, which many expect would be in the billions.

The government has previously declined to say whether the government plans to offer disability pensions exactly the same as those offered to veterans before 2006, or whether they will be retroactive.

Around 70,000 injured veterans received a total of about $2.8 billion in lump-sum payments between 2006 and February 2016 and many of them have indicated they would have preferred a pension.

Some veterans groups have conceded that the old disability pensions are gone for good and that it's inevitable something different will replace them.