05/16/2012 16:05 GMT

NAIROBI, May 16, 2012 (AFP) - Diplomats are working to push foes Sudan and South Sudan to resume negotiations after missing a UN deadline for face-to-face talks, the US government's top diplomat for Africa said Wednesday.

"While there has not been a full resumption of discussions between the two sides, things are being done," said Johnnie Carson, assistant secretary of state for African affairs.

"We want them to be done much faster, and with greater alacrity and commitment," Carson said, speaking from Washington to reporters across Africa in a telephone press conference.

The UN Security Council resolution on May 2 gave Sudan and South Sudan two weeks -- until May 16 -- to unconditionally resume the talks.

The unanimous resolution threatened sanctions if its demands are not complied with.

It sought to avert a "serious threat to international peace and security" caused by the situation along the disputed border between the two countries, after weeks of fighting.

Former South African president Thabo Mbeki, who is heading African Union-led talks, is in contact with both sides to encourage the end of a bitter dispute over issues that include oil transit fees and contested border zones, Carson said.

"They must sit down and seriously negotiate their differences, and recognise that they cannot make progress on the battlefield," Carson added.

"They have to come to the table and meet on a regular basis, and live up to the commitments that they make."

Sudan's President Omar al-Bashir, an accused war criminal, said last week that his country "will not negotiate about any issues" unless security matters are resolved first.

The South's lead negotiator, Pagun Amum, told AFP Tuesday that his country is ready to resume the African Union-led talks.

On Wednesday the International Committee of the Red Cross (ICRC) warned of "mounting humanitarian needs in South Sudan" in conflict-hit border regions, calling on both sides to "respect civilians, the wounded and prisoners."

The South separated last July with about 75 percent of the former united Sudan's oil production, but Juba still depended on the north's pipeline and Red Sea port to export its crude.

A protracted dispute over fees for use of that infrastructure led South Sudan in January to shut its oil production after accusing the north of theft.

The Security Council gave both sides three months to conclude the talks.