U.S. President Donald Trump says military personnel have deployed to Central Africa in advance of possible "violent demonstrations" in Congo over results of Sunday's presidential election.

Trump's letter to House Speaker Nancy Pelosi says about 80 military personnel and "appropriate combat equipment" deployed to nearby Gabon to support the security of U.S. citizens and staffers and diplomatic facilities in Congo.

Trump's letter says more military personnel will deploy as needed to Gabon, Congo or neighboring Republic of Congo.

Congo faces what could be its first democratic, peaceful transfer of power since independence from Belgium in 1960, but election observers and the opposition have raised concerns about voting irregularities.

The powerful Catholic church has said its data show a clear winner, angering Congo's ruling party.

First results are expected on Sunday.