Clinton, the front-runner for the party's nomination in the Nov. 2016 contest, made the comments while campaigning in Iowa, where her lead has slipped in recent weeks ahead of the state's early voting contest.

"I am worried about certain recipients because I think it's important to enhance the benefits," the Journal reported Clinton as saying at a campaign event in the city of Decorah.

"We do have to extend the life of the trust fund and that's going to take some new funding," she said.

The newspaper reported that Clinton would consider raising to an undisclosed amount the maximum income that would be subject to the 6.2 percent Social Security tax.

Under the current rule, money made from investments, as well as pensions, annuities and interest, are not considered income, and only the first $118,500 wages are subject to the tax.

Fears over the solvency of the Social Security system have made it an important election issue.

Clinton's main rival for the Democratic nomination, Bernie Sanders, has described Social Security as the nation's "most successful government program," and has called for its expansion, which he says will be paid for by lifting the cap on taxable income above $250,000.

Voters in Iowa will cast some of the country's earliest ballot's in the caucus nominating contest on Feb. 1.