KHARTOUM, Oct 28 (Reuters) - Hours before Sudan"s army seized power and dissolved its government, a senior U.S. envoy warned the country"s top general not to take any steps against the civilian administration that was overseeing a democratic transition, diplomats said. Jeffrey Feltman, President Joe Biden"s special envoy for the Horn of Africa, flew into Khartoum two days before Monday"s coup, as concerns mounted that the transition was running into trouble due to mounting tension between the generals and civilians. But instead of heeding the warning, the army did just the opposite, acting on a plan to seize power that two diplomats and three Sudanese official sources said had been developed over the preceding weeks. The coup brought an abrupt halt to a political transition that began after a popular uprising led to the overthrow of former President Omar al-Bashir in 2019, and was meant to end with elections in late 2023. After Feltman flew out, uniformed soldiers rounded up the civilian cabinet in pre-dawn raids, before Gen Abdel Fattah al-Burhan announced the dissolution of the government. Until the last moment, the military was hoping to persuade Prime Minister Abdalla Hamdok to dismiss his cabinet so they could tighten their grip on the transition without using force while keeping him in office, according to the diplomats and two of Hamdok"s aides. Hamdok refused to cooperate. The decision to ignore warnings from the United States -- which had thrown diplomatic and financial weight behind the transition -- and move forward with what one of the diplomats and Sudanese sources with knowledge of the matter described as a "plan B" without Hamdok, reflected the stakes for the army, which analysts say saw growing risks from continued civilian rule. In his last meeting with Burhan, Feltman "put Burhan under big pressure not to do anything against the cabinet, to de-escalate", said one diplomat briefed on the meeting, declining to be identified. But Burhan was also under pressure from factions in the army and his deputy in the Sovereign Council that had been steering the transition, the powerful head of the paramilitary Rapid Support Forces (RSF), to take a hard line with the civilians, the diplomat said. "During the meeting they decided to go with Plan B. This was the last chance to get Hamdok to take part," he said. Sudan"s military did not respond to calls seeking comment. The U.S. State Department did not immediately respond to questions from Reuters about Feltman"s meetings in Khartoum. Feltman received no heads-up about the military intervention, State Department spokesman Ned Price told reporters on Monday. "It is not something that we were apprised of beforehand by anyone, and we would have made very clear of the profound implications that any such move would have," he said. Feltman had urged authorities to agree a date for transferring leadership of the Sovereign Council from Burhan to a civilian and to initiate security sector reform, the State Department said before the coup. DERAILING DEMOCRACY The military has been at the heart of power in Sudan since independence in 1956, staging repeated coups that snuffed out occasional experiments with civilian control. Bashir, a general, seized power in one such coup in 1989, and ruled for three decades during which Sudan became an international pariah. He hosted Osama bin Laden in the 1990s and fought wars against restive regions, for which he was indicted in the Hague on genocide charges he denies. After decades of conflict, he allowed the country"s mainly non-Arab south to gain independence in 2011. But peace did not bring prosperity. Oil revenue dwindled, economic output per capita cratered, and by 2019, hundreds of thousands of mainly young demonstrators had taken to the streets to demand his removal. It was the army that finally deposed him. Under the power sharing deal that followed, the military was due to hand over leadership of the transition to civilian groups in the coming months. But the partnership became increasingly strained by demands for the military to be brought under civilian control, for justice over protester deaths during the uprising, and by the government"s agreement to hand Bashir and others to the International Criminal Court. Feltman"s visit followed weeks of escalation and signs of deepening splits, both between civilians and the military and within the army. read more Protests by a tribal group blocked essential imports at the country"s main port, Port Sudan. Matters came to a head after Sept. 21, when authorities said they had thwarted a coup plot attributed to mutinous military factions and Bashir loyalists. On Oct. 16, rebel groups and parties aligned with the military began a sit-in in Khartoum, calling on the military to dissolve the government. In response, opponents of a military takeover held huge rallies on Oct. 21. The United Nations special envoy to Sudan, Volker Perthes, said he met with a military leader from the Sovereign Council late on Sunday afternoon and that they discussed a possible U.N.-led dialogue. "He also indicated that the military might move, of course ... I strongly warned against doing this," Perthes told reporters. Hamdok was still meeting with Burhan at army headquarters at 8 p.m. on Sunday, hours before he was placed under house arrest, said Adam Hereika, Hamdok"s chief of staff. Hamdok refused to dissolve the government without a political process, Hereika told Reuters. "They were insistent on changing the government and having the government follow their orders," he said. Burhan told reporters on Tuesday that he had discussed with Feltman political divisions that "threaten the country"s security", and that he had offered Hamdok several options for resolving the crisis. RUSSIAN "GREEN LIGHT" The United States has responded with condemnation and a decision to freeze $700 million of economic assistance for Sudan. Washington had swung firmly behind the transition, removing Sudan from its list of states that sponsor terrorism and providing diplomatic support that helped secure billions of dollars worth of debt relief. Though U.S. ties have been shaken, Burhan can likely still depend on the backing of U.S.-allied Arab states with whom he has developed close relations. These include Saudi Arabia, the United Arab Emirates and Egypt, which were all happy to see the downfall of Bashir, whose Islamism they opposed. The army may also be looking to build closer ties with Russia: diplomats and analysts say RSF commander General Mohamed Hamdan Dagalo has cultivated ties to Moscow. Ahead of the coup, the military sought and obtained a "green light" from Moscow in an effort to protect themselves from any sanctions imposed through the United Nations Security Council, two official Sudanese sources said. The Kremlin responded to the coup by urging all parties to show restraint and calling on Sudanese to resolve the situation on their own as quickly as possible and without any loss of life. But it did not condemn the takeover. The Russian Foreign Ministry did not immediately respond to a request for comment on its Sudan policy. Russia already appears to be shielding Sudan"s military in a possible Security Council statement. Two diplomats with direct knowledge of negotiations on the text said Russia had suggested the 15-member council express concern at developments in Sudan, rather than condemn the takeover. Negotiations on the text, which has to be agreed by consensus, are ongoing. Western states that backed the transition will need to re-evaluate how to apply pressure on Sudan, said Jonas Horner of the International Crisis Group. "I think it"s probably been very chastening for Sudan"s Western allies. The military brushed aside what was being held over their heads in the end," he said.