NEW : South Sudan becomes Africa 's newest state . It recognizes the sovereignty of the Sudan , within the 1956 borders . Those borders put the contested town of Mara in the north . A new U.N. military mission will step in .
NEW : South Sudan becomes world 's newest country . Khartoum recognizes the sovereignty of the South , within the 1956 borders . Those borders put the contested region of Abyei in the north . A new U.N. peacekeeping mission will step in .