The new nation of South Sudan has formally declared its independence.

Speaker of parliament James Wani Igga read the official declaration Saturday in front of hundreds of thousands gathered for ceremonies in the capital, Juba.

The crowd roared as soldiers raised the new Southern Sudanese flag and lowered the flag of the north. President Salva Kiir then took the oath of office, swearing to uphold the constitution and to foster the development and welfare of South Sudan's people.

The Republic of South Sudan became the world's newest country at midnight local time. Residents of Juba celebrated with parties in the streets.

The celebration continued with ceremonies at a Juba stadium named after John Garang, who led southern forces during the long Sudanese civil war.

A long list of dignitaries are addressing the crowd. U.N. chief Ban Ki-moon said South Sudan's people have claimed hold of the dignity and freedom that are their birthright.

The head of the U.S. delegation, Ambassador Susan Rice, said South Sudan's future depends on strong government institutions that are free of corruption.

Southern Sudan voted overwhelmingly to split from the north in a January referendum. The vote stemmed from a 2005 peace deal that ended the two-decade civil war.

Already, South Sudan has been recognized by its northern neighbor. Sudan's minister for presidential affairs, Bakri Hassan Saleh, made the official announcement Friday. Egypt and the United States followed with recognition on Saturday.

The declaration of independence, approved by South Sudan's parliament, calls for a system of governance that upholds rule of law, justice, democracy, human rights and respect for diversity.

In the background of Saturday's festivities there are many challenges the new nation will face.

South Sudan has been wracked with deadly violence, and has yet to resolve disputes with the north on borders and how to share oil revenue.

On Friday, the U.N. Security Council approved a new peacekeeping force for South Sudan. The force will have up to 7,000 troops and 900 civilian police.