Sudanese President Omar al-Bashir has sent a letter to the UN secretary-general challenging a plan to send UN peacekeepers to Darfur - a setback to international efforts to stop the region's escalating violence. The UN wants to send a 22,000-member joint UN-African Union peacekeeping mission to Darfur, arguing the AU force of 7,000 now on the ground is overwhelmed. Al-Bashir agreed to the plan in November but has since sent conflicting signals about his commitment. In his letter, obtained Friday, al-Bashir insisted the November agreement established that the UN would provide the AU force with technical and financial assistance and "military consultants with ranks below that of the military commander appointed by the African Union." He objected to a section of a UN report stating that "full UN involvement in command and control would be a prerequisite for UN funding and troop contribution." Secretary-General Ban Ki-moon received the letter Thursday, nearly two months after he asked al-Bashir to express his commitment to the plan in writing, said UN spokeswoman Marie Okabe. Okabe said the letter, dated March 6, "contains some elements which seem to challenge the agreements reached last November ... on peacekeeping in Darfur." She said Ban would consult with the UN Security Council on how to respond.