U.S. Senate lawmakers have ordered federal investigators to examine foreign state-run investment funds and whether the much-needed capital infusions being provided to major U.S. banks raises any economic or security concerns.

The Government Accountability Office this week began an investigation into sovereign wealth funds, including the size and types of investments funds are making in U.S. markets, a spokeswoman said.

The probe, which was requested by the Senate Banking, Housing and Urban Affairs Committee, will also examine what oversight - both international and in the U.S. - is conducted on the funds and whether the funds pose a risk to U.S. economic stability.

The state-run funds, primarily those located in Asia and Middle East, have made headlines in recent months by acquiring stakes in major banks such as Merrill Lynch & Co. (MER), Citigroup Inc. (C), and UBS AG (UBS), a major Swiss bank with extensive U.S. operations.

Both Merrill and Citi, which have already received billions in cash infusions from the funds, are currently in talks to receive even more capital from outside investors.

That has raised eyebrows on Capitol Hill, where lawmakers have aggressively scrutinized foreign investments in U.S. companies in recent years. The most notable case involved Dubai-controlled DP World. In 2006, federal approval for the firm to manage six U.S. ports sparked a firestorm of controversy and led lawmakers to pass a law overhauling the review process for foreign investments in the U.S.

The role of sovereign wealth funds has yet to reach the same level of scrutiny as the ports deal, but the GAO investigation could signal lawmakers will focus more attention on the issue when they return to Washington this month.

In addition to the Senate Banking panel, House Financial Services Chairman Barney Frank, D-Mass., is also expected to have his committee conduct oversight hearings on the funds this year.

U.S. lawmakers are not alone. A number of European governments have said they are drafting proposals limiting or blocking foreign state-run investments.