UNITED NATIONS - The United States is worried about the flow of arms into semi-autonomous Southern Sudan, some of it heavy weapons, ahead of a nationwide April election, the US envoy to the United Nations said.

"Heavy munitions seem to be flowing in," US ambassador Susan Rice said after a UN Security Council meeting on Sudan on Tuesday.

She said the region had "porous borders" with arms coming from "all directions".

Human Rights Watch warned on Sunday that repression of political opponents in both the North and South was undermining prospects for Sudan's first democratic elections in 24 years, scheduled for April.

After decades of north-south civil war, a 2005 peace deal outlined the elections.

But delays in implementing the deal have fueled mistrust and a recent law forced through by president Omar Hassan al-Bashir's giving Sudan's intelligence unit wider powers has worsened matters.

Rice said the elections needed to be credible and UN peacekeepers would have to do their best to provide security.- Reuters