President George W. Bush said Tuesday that a rigorous effort should be made to fully carry out a fragile 2005 peace agreement in Sudan that ended a 21-year civil war between the ethnic African south and the Arab-dominated government in the capital Khartoum.

In a statement marking the third anniversary of the accord on Wednesday, Bush specifically said a nationwide census should be conducted immediately to allow national elections to be held on time next year.

"The work of Sudan's border commission also must be invigorated to redeploy troops away from disputed border areas to reduce the changes of a return to violence," Bush said.

Under the peace agreement, all troops are supposed to withdraw from the border zone to allow it to be patrolled by 10,000 U.N. peacekeepers along with joint units of northern and southern forces. The two sides only began allowing the U.N. to begin patrol in December in the Abeyi area, which contains some of Sudan's richest oil fields and is contested by both sides.

Bush said he had asked his new special envoy for Sudan, Richard Williamson, "to continue the United States' strong involvement on north-south issues to help find solutions to these challenges."

He said Williamson also must advance efforts to end violence in the eastern Darfur region, "Where innocent civilians continue to fall victim to the scourge of government-and rebel-led attacks."

Bush said the United States was firmly committed to the rapid deployment of an effective U.N.-African peacekeeping force coupled with serious political dialogue between the parties to help end the Darfur crisis.

In Darfur, ethnic African rebels rose up against the Khartoum government in 2003, sparking a conflict that shows no sign of ending. A new U.N.-African force was launched last week, but many fear it may not be strong enough to stop the violence amid resistance from Sudan"s government.

If the north-south peace should collapse and fighting between the two sides resumes, the resulting chaos would likely intensify the Darfur conflict as well.

The dispute over the Abeyi oil fields has already shaken the peace deal once. Last October, southern Cabinet ministers walked out of the unity government over a number of disputes,including the oil fields, raising fears the peace accord could collapse.

The ministers rejoined the government in late December having settled most of their differences, except the oil fields.

Abeyi lies just north of the boundary line between north and south Sudan set by British colonial rulers in the early 20th century. But the line is disputed, and southerners want the area incorporated into their autonomous zone, created by peace agreement.

The government in Khartoum, unwilling to let go of the lucrative oil fields, has rejected a proposed new boundary recently drawn by an international commission that would put Abeyi in the south.