"The freedom of religion is a constitutional right. Where a place of worship is located is a local decision," the top congressional Democrat said in a statement on what has become a national political debate.

Pelosi said she backed calls for transparency regarding who is funding the project -- an Islamic community center two blocks from "Ground Zero" -- but that it was also necessary to know who was bankrolling opposition to it.

Republicans have denounced the planned mosque construction on grounds that building a Muslim place of worship near where Islamic extremists attacked the United States offends the memory of the victims of 9-11.

Some critics have also cited opposition from some relatives of those killed in the strikes that brought down the World Trade Center's twin towers -- though some victims' family members have also backed the project.

Pelosi urged "all of those expressing concern about the 9/11 families" to support legislation -- opposed by Republicans -- aimed at helping emergency workers coping with serious health problems stemming from their exposure to hazardous materials when they responded to the attacks.

Her comments came after the top US Senate Democrat, Majority Leader Harry Reid, said the center "should be built someplace else" in response to pressure on the issue from his Republican challenger in the November elections.

Pelosi's statement largely echoed President Barack Obama's own remarks on the issue, which played up the US Constitution's guarantee of freedom of religion while omitting any explicit endorsement or criticism of the project.

Republicans have served notice that they plan to challenge Democrats on the issue in the run up to the November elections that will decide control of the US Congress.