A controversial oil exploration deal between Iraq's autonomy-minded Kurds and a Norwegian company got underway this week without the approval of the central government here, raising a potentially explosive issue at a time of heightened ethnic and sectarian tensions.

The Kurdistan Democratic Party, which controls a portion of the semiautonomous Kurdish enclave in northern Iraq, last year quietly signed a deal with Norway's DNO to drill for oil near the border city of Zakho. Iraqi and company officials describe the agreement as the first involving new exploration in Iraq since the U.S.-led invasion in 2003.