By Michelle Nichols

UNITED NATIONS (Reuters) - Political uncertainty over Democratic Republic of Congo's next presidential election could spiral into a severe crisis and United Nations peacekeepers are developing contingency plans for widespread violence, Secretary-General Ban Ki-moon has warned.

In a report to the U.N. Security Council released on Tuesday, Ban said that under those plans peacekeepers in Congo might need to ask for help from other U.N. missions.

"I am concerned that in the absence of a credible and meaningful political dialogue among Congolese stakeholders, tensions could degenerate into a severe crisis, with a high risk of relapse into violence and instability," Ban said.

The Congolese government has said it is unlikely it will be able to hold elections in November for logistical reasons but opponents of President Joseph Kabila accuse him of trying to cling to power. The government has denied the claim.

Kabila, who has been in power since 2001, is barred by the constitution from standing for a third term. But a Kabila ally has raised the prospect of a referendum to allow him to run.

Dozens of Kabila's critics have been arrested since last year as part of what the United Nations and rights groups say is an escalating crackdown on political dissent ahead of a presidential election.

"I urge the government of Democratic Republic of Congo to respect freedom of expression, assembly and information as fundamental rights that are essential to the conduct of free and fair elections," Ban said.

Dozens died in street protests in January 2015 against a revision to the election code that could have pushed the election back by years.

"(The U.N. peacekeeping mission) MONUSCO is developing contingency plans in the event of widespread violence in the context of the electoral process," Ban said.

The U.N. Security Council is due to be briefed on the U.N. peacekeeping mission on Thursday.

The overthrow of longtime Congolese ruler Mobutu Sese Seko in 1997 fuelled years of conflict in the mineral-rich east that sucked in more than half a dozen countries and killed millions of people. U.N. peacekeepers have been deployed in Congo since 2000.

(Reporting by Michelle Nichols; Editing by Phil Berlowitz)