U.N. Secretary-General Kofi Annan said on Thursday Darfur was close to a catastrophe, Reuters reported. Annan, in his monthly report on Sudan's vast Darfur region, said violence, rape and insecurity were on the rise, despite a peace agreement between the government and one rebel group. "The region is again on the brink of a catastrophic situation," he wrote. "Unless security improves, the world is facing the prospect of having to drastically curtail an acutely needed humanitarian operation," Annan said. The United States demanded that the Security Council respond to Sudan's warning that any nation pledging U.N. troops for Darfur was committing a "hostile act" and a "prelude to an invasion." The warning came in an unsigned letter on Thursday from Sudan's U.N. mission to dozens of countries, many of whom attended a meeting on September 25 on potential pledges of troops to a U.N. force in Darfur. "In the absence of Sudan's consent to the deployment of U.N. troops, any volunteering to provide peacekeeping troops to Darfur will be considered as a hostile act, a prelude to an invasion of a member country of the U.N," the letter said. In response, U.S. Ambassador John Bolton circulated a draft statement, obtained by Reuters, that Security Council members will consider on Friday. It says the council "deplores" the Sudan mission's attempt "to intimidate potential troop-contributing countries volunteering forces for a peacekeeping mission in Darfur." Bolton noted that the diplomatic note was inconsistent with a polite letter Sudan's President Omar Hassan al-Bashir wrote to Annan this week welcoming U.N. logistics and other support to the AU mission in Darfur.