U.S. President Barack Obama has offered the Sudanese government "incentives" to improve conditions on the ground in Darfur and southern Sudan, but promised to renew tough sanctions if the effort fails.

Sudanese President Omar al-Bashir, pictured in March, was charged by the International Criminal Court with committing crimes against against humanity and allegedly masterminding deadly attacks throughout Darfur. (Associated Press)

"If the government of Sudan acts to improve the situation on the ground and to advance peace, there will be incentives. If it does not, then there will be increased pressure imposed by the United States and the international community," Obama said in a statement Monday.

"As the United States and our international partners meet our responsibility to act, the government of Sudan must meet its responsibilities to take concrete steps in a new direction."

The U.S. and international community must act "with a sense of urgency and purpose" to seek an end to hostilities, human rights abuses and genocide in Sudan's Darfur region, Obama said. He said an agreement between the country's warring north and south must be implemented for there to be any chance for long-term peace.

The urgency was underscored Monday when peacekeepers in Darfur, in the west part of the country, noted a sizable and unusual increase in military activities by Sudanese government forces and a Darfur rebel group in northern Darfur.

The United Nations-African Union Mission in Darfur expressed grave concern about the buildup "as it may signal the impending start of a new cycle of armed confrontations in the area." Peacekeepers in the region have seen a buildup of military matériel and personnel, as well as the digging of trenches by government forces and rebels from the Sudan Liberation Army's Abdul Wahid faction, mission spokesman Kemal Saiki said.

Susan Rice, the U.S. ambassador to the UN, and Scott Gration, the U.S. envoy to Sudan, have clashed over how far to engage the Sudanese government of President Omar al-Bashir. Bashir is charged by the International Criminal Court with crimes against humanity and war crimes on allegations he masterminded deadly attacks throughout Darfur.

Gration has argued in public for a less strict line toward Bashir, saying he is the key to resolving the situation in Darfur as well as in southern Sudan. Rice favors taking a hardline approach.

However, the new U.S. policy will not make major concessions to Bashir, U.S. officials said last week, speaking on condition of anonymity because Congress had yet to be briefed on the planned policy shift. Bashir's government is designated a "state sponsor of terrorism" by the U.S. State Department.

The Darfur conflict began in February 2003 when black Africans took up arms against the Arab-dominated government in Khartoum, claiming discrimination and neglect.

UN officials say the war has claimed at least 300,000 lives from violence, disease and displacement. They say some 2.7 million people were driven from their homes and at its height, in 2003-2005, it was the world's worst humanitarian crisis.