By Michelle Nichols

UNITED NATIONS (Reuters) - The United Nations doubts the willingness of the South Sudan government to cooperate with the deployment of thousands more peacekeepers and urged the Security Council to apply "credible pressure," according to a report seen by Reuters on Tuesday.

Following fierce fighting in the capital, Juba, in July, the 15-member Security Council authorized a 4,000-strong regional protection force in August as part of the U.N. peacekeeping mission and threatened an arms embargo if the government did not cooperate or stop hindering the movement of peacekeepers.

None of the troops for the protection force have yet been deployed and South Sudan's defense minister, information minister and a presidential security adviser all questioned last week whether there was a need for the additional troops.

"These statements by key officials in charge of defense and security shed doubt on the (government's) actual willingness to actively cooperate with the deployment and operationalization of the force, unless credible pressure is applied by the council and the region to support it," U.N. Secretary-General Antonio Guterres said in a confidential report to the Security Council.

The Security Council failed last month to adopt a U.S.-drafted resolution to impose an arms embargo and further sanctions on South Sudan despite warnings by U.N. officials of a possible genocide in the world's newest state.

Political rivalry between President Salva Kiir, an ethnic Dinka, and Riek Machar, his former deputy, led in 2013 to civil war that often has followed ethnic lines. Machar, a Nuer, fled in July and is now in South Africa.

Guterres' report said the government needed to issue visas for advance teams linked to the deployment of the regional protection force. He said if those visits could be completed by the end of January, the first troops for the force could be on the ground by the end of February or in March.

U.N. peacekeepers have been in South Sudan since the nation gained independence from Sudan in 2011, and there are currently some 12,800 U.N. troops and police in the country.

"The trend of bureaucratic impediments and restrictions continues to constrain the mission's capacity to carry out it's mandated tasks ... and its ability to project presence in locations where civilians are in need of protection, including from ethnically driven attacks," the Jan. 16 report said.

(Reporting by Michelle Nichols; Editing by Peter Cooney)