South Sudan's President Salva Kiir on Saturday told thousands of jubilant southerners that their martyrs had not died in vain and that the newborn nation's Independence Day would always be engraved on their hearts.

"Our martyrs did not die in vain... We have waited for more than 56 years for this day. It is a day that will be forever engraved on our hearts and minds," Kiir said in a speech that was met with roars of approval.

World leaders on Saturday hailed the birth of the world's newest nation, the Republic of South Sudan, as a historic event bringing to a close 50 years of conflict in northeastern Africa.

U.S. President Barack Obama led official recognition of the country, calling it "another step forward in Africa's long journey toward opportunity, democracy and justice."

Sudan's Omar al-Bashir said on Saturday that the newly independent Republic of South Sudan's success "will be our success," and renewed his call for an end to U.S. sanctions against his country.

"We fulfill our commitment to help the new state of South Sudan in its first steps, because we want it to succeed, and because its success will be our success," Bashir said in a conciliatory speech to tens of thousands of southerners at the official independence ceremony in Juba.

Celebrations erupted in South Sudan on Saturday as the world's newest nation proclaimed formal independence and turned the page on five decades of devastating conflict with the north.

"Our martyrs did not die in vain... We have waited for more than 56 years for this day. It is a day that will be forever engraved on our hearts and minds," President Salva Kiir told tens of thousands of jubilant southerners at the official ceremony in Juba.

Sudan's President Omar al-Bashir on Friday ordered the army to fight in South Kordofan until it has "cleaned" the border state of rebels, in a speech just eight days before the south secedes.

"I ordered the Sudanese Armed Forces to continue their operations in South Kordofan until they clean the state of rebels," Bashir told the faithful at a mosque in Khartoum during Friday prayers, in a speech broadcast on state television.

Sudan's government agreed Tuesday to appoint a vice president from the war-torn Darfur region, taking a step toward satisfying a key rebel demand for greater power-sharing, state media reported.

"The government agrees to appoint a vice president from (the) Darfur region to complete the current electoral term," SUNA news agency said in a brief statement.

A deal reached this week between Khartoum and a branch of the ex-rebel Sudan People's Liberation Movement aims for a full ceasefire to end fighting in South Kordofan, an SPLM minister said Wednesday.

The two sides signed the deal on Tuesday to resolve their differences in the embattled border state, where heavy fighting has raged for around two weeks.

The U.N. Security Council on Monday unanimously voted to send a 4,200-strong Ethiopian peacekeeping force to the disputed Sudanese territory of Abyei.

The force will monitor the withdrawal of north Sudan troops from Abyei as well as human rights in the region.

President Barack Obama called Wednesday for an immediate ceasefire in Sudan's South Kordofan state, where he said the situation is "dire" with government forces accused of ethnic cleansing.

Heavy fighting in the run-up to south Sudan's declaration of independence on July 9 has pitted government troops and allied militias against forces aligned with the southern Sudan People's Liberation Army (SPLA).

The rival governments of north and south Sudan signed an accord Monday on the demilitarization of the disputed Abyei frontier region, mediator Thabo Mbeki told the U.N. Security Council.

The former South African president, who heads an African Union panel mediating on Sudan, said the accord had been signed "in the last hour" before his address to the Security Council by video link from Addis Ababa.