The presidents of Sudan and Chad signed a peace agreement Thursday to prevent armed groups operating along their shared borders from destabilizing the region, officials said. The deal came even as Chad accused Sudan of backing a new rebel advance into its territory. The agreement, signed by Sudan's Omar al-Bashir and Chad's Idriss Deby, commits the two nations to implementing past accords that have so far failed to help end violence in the area. It calls for the establishment of a monitoring group of foreign ministers from each country that would meet monthly to be sure there are no violations. If successful, though, it would only be a small step toward ending violence in Sudan's Darfur region. A text of the deal said the two leaders agreed to "inhibit all activities of armed groups and prevent the use of our respective territories for the destabilization of one or the other of our states."