U.S. President Barack Obama threatened on Friday that there must be consequences for Sudan and its leaders if a referendum on the future of southern Sudan is not held on time and peacefully. Obama made the warning at a United Nations ministerial meeting on Sudan. 'The Comprehensive Peace Agreement (CPA) that ended the civil war must be fully implemented; the referenda on self-determination scheduled for Jan. 9 must take place -- peacefully and on time; the will of the people of South Sudan and the region of Abyei must be respected, regardless of the outcome,' he said. 'The choice is for Sudanese leaders -- whether they will have the courage to walk the path. And the decision cannot be delayed any longer.' Despite some recent progress, preparations for the referendum are still behind schedule, said Obama. He threatened that if the Sudanese leaders 'flout their responsibilities,' there must be consequences, which could mean more pressure and deeper isolation. Obama said if they fulfill their obligations, relations between the United States and Sudan will improve. On Jan. 9, 2011, the southern Sudanese are expected to vote in a referendum for unity with north Sudan or separation according to the Sudanese Constitution and the provisions of the CPA, inked between the Sudan People's Liberation Movement (SPLM) and the National Congress Party (NCP) in 2005, which ended the longest civil war in Africa. Washington has long been pushing for the happening of the referendum. On Sept. 14, it announced a package of new incentives, which include full normalization of relations, lessening Sudan's debts, lifting the sanctions and removing Sudan from the U.S. list of so-called countries harboring terrorism. Washington's incentives were rejected by the Sudanese government. 'We have expressed our stance towards such offers earlier. We reject in principle the issue of incentives and pressures. This is an unacceptable matter,' Sudanese presidential adviser Ghazi Salahuddin told reporters on Sept. 15. 'If there is a constructive plan from the United States to develop the relations between the two countries and actively contribute to the resolution of the Darfur issue, we will look into such a constructive plan. But to present matters as reasons or approaches to impose sanctions or give incentives, then this method is unacceptable', he said. Sudanese President Omar al-Bashir on Wednesday reiterated his government's commitment to a free, fair and distinguished referendum for southern Sudan. However, a number of issues remain unsolved, which cast doubt on the possibility of conducting the referendum. According to the CPA, the south Sudan referendum is to be coincided with another referendum on the oil-rich Abyei area where citizens of Abyei would decide whether to remain part of the north or join the south. The SPLM and the NCP, however, have not yet agreed on members of Abyei referendum commission. 