* U.N. Development Programme heads ordered out

* U.N. chief Ban urges Sudan to reverse decision

* Latest move against U.N. agencies by Khartoum (Adds U.N. statement)

KHARTOUM, Dec 26 (Reuters) - Sudan has ordered two senior United Nations officials to leave, the world body said on Thursday, in what appeared to be an escalation of President Omar Hassan al-Bashir's move against U.N. activities in the country.

The United Nations said in a statement that the officials are Ali Al-Za'tari, U.N. resident coordinator at the United Nations Development Programme; and Yvonne Helle, the UNDP's country director.

U.N. spokesman Stephane Dujarric said in the statement that Secretary-General Ban Ki-moon condemned Khartoum's demand for the exit of the two senior UNDP officials.

"The sanctioning of United Nations personnel sent to Sudan to carry out their duties in accordance with the United Nations Charter is unacceptable," Dujarric said.

"The Secretary-General calls on the government of Sudan to reverse its decision immediately and urges it to cooperate fully with all United Nations entities present in Sudan," he added.

The reason for the expulsions was not immediately clear, but they come a month after Bashir called for peacekeepers from UNAMID, the joint U.N.-African Union Mission in Darfur, to leave, calling them a "security burden."

Sudan had already shut UNAMID's human rights office in Khartoum and called on the mission to prepare an exit plan. The move came days after it denied peacekeepers permission to pay a second visit to the site of alleged mass rapes by Sudanese soldiers in Tabit, a village in Darfur, the western region plagued by conflict.

The head of the U.N. peacekeeping forces said UNAMID was unlikely to bow to Sudan's request to leave when the situation there appears to be worsening.

Conflict erupted in Darfur in 2003 when mainly African tribes took up arms against the Arab-led government in Khartoum, accusing it of discriminating against them. UNAMID has been deployed in Darfur since 2007.

The UNDP, based in New York, deferred to U.N. spokesman Dujarric for comment. Sudan's Foreign Ministry declined to comment.

Contacted by email, the UNDP's Helle also declined to comment. Za'tari was not immediately available.

U.N. sources said Helle, a Dutch national, had been told to leave Sudan by Dec. 29, and Za'tari, a Jordanian, would depart by Jan. 2. (Reporting by Khalid Abdelaziz; Additional reporting Lin Noueihed and Louis Charbonneau; Writing by Mahmoud Mourad; Editing by Stephen Kalin, Robin Pomeroy, Pravin Char, Dan Grebler and Mohammad Zargham)