By the BBC State Department correspondent Richard Lister

The United States is to send a high level delegation to Nigeria within the next two weeks to urge the military leader, General Sani Abacha, to implement democratic reforms.

Washington is becoming increasingly worried about the deteriorating situation in Nigeria in the run-up to presidential elections in which General Abacha is the sole candidate.

Announcing this mission, the state department spokesman, James Rubin, described the process under which General Abacha is supposed to be handing control to a civilian government as flawed and failing.

Nigeria has been by-passed during recent high-level American visits to Africa, as a mark of Washington's displeasure with General Abacha's regime.

But Mr Rubin said it was now important to try to reduce the risk of greater insecurity in Nigeria.

Washington wants credible transition

"The delegation's visit does not signify a shift in our policy, but rather an intensification of our efforts to share our concern about the situation in Nigeria and to urge swift movement towards a credible process leading to democratic civilian government.

"It is not a negotiating session, or a bargaining session, but an open discussion of concern between our two nations," he said.

Despite the fact that Nigeria is a major oil supplier to the United States, it is subject to a range of American sanctions because of its human rights record and failure to open its political process.

The delegation, to be led by the Under-Secretary of State, Thomas Pickering, is expected to emphasise to General Abacha that the United States will keep Nigeria at arm's length, unless he presides over a genuine transition to civilian democracy.