AMMAN (Reuters) - Syrian tanks occupied the main square in central Hama on Wednesday after heavy shelling of the city, residents said, taking control of the site of some of the largest protests against President Bashar al-Assad. Human rights campaigners say more than 90 people have been killed in Hama since Assad launched a military assault on Sunday to regain control, triggering international condemnation and calls from U.S. senators for sanctions on Syria's energy sector. At the United Nations, a diplomat said the Security Council had "substantially agreed upon" a draft statement that would condemn human rights violations and use of force against civilians by Syrian authorities. The council diplomat said the statement could be adopted later on Wednesday. Meanwhile, the United States Wednesday said it had no interest in seeing Syria's President Bashar al-Assad survive simply to preserve regional "stability," hardening its line on what it termed a "grotesque" crackdown on dissent. Some analysts have speculated that Washington has been wary of directly calling for Assad to quit because of anxiety that security chaos, civil war and a Middle East power vacuum might follow the demise of his regime. But White House spokesman Jay Carney said Wednesday that Washington did not view Assad as "indispensible," saying he was completely "incapable and unwilling" to respond to the grievances of his own people. "The US has nothing invested in Assad remaining in power. We do not want to see him to remain in Syria for stability's sake and rather we view him as the cause for instability in Syria," Carney said. "All communications have been cut off. The regime is using the media focus on the Hosni Mubarak trial to finish off Hama," one resident told Reuters by satellite phone from the city. He said tanks and military units including paratroopers and special forces were seen moving to the central Orontes Square from the south, accompanied by militia known as 'shabbiha'. Residents said shelling concentrated on al-Hader district, large parts of which were razed in 1982 when Assad's late father President Hafez al-Assad crushed an armed Islamist uprising, killing thousands. Authorities say the army has entered Hama to confront gunmen who were intimidating residents. State television broadcast footage of armed men in civilian clothes who it said had attacked security forces and government buildings. Syria has expelled most independent media, making it difficult to verify accounts from activists and authorities. The plight of Hama has prompted many Syrians to stage solidarity marches since the start of the holy month of Ramazan earlier this week. But Assad's response suggests he will resist calls for change that have swept Syria and much of the Arab world, and has led to Western calls for tougher international measures. "The United States should impose crippling sanctions in response to the murder of civilians by troops under the orders of President Assad," U.S. Senator Mark Kirk said on Tuesday. Kirk, a Republican, was introducing legislation in Washington to target firms that invest in Syria's energy sector, purchase its oil or sell gasoline. His bill was also sponsored by Democratic Senator Kirsten Gillibrand and independent Senator Joseph Lieberman, who said it was time to push for "a democratic transition that reflects the will of the Syrian people." Washington says Assad has lost legitimacy and has imposed sanctions on the president and his top officials, but has stopped short of directly calling on him to leave office as it did to Mubarak and Libya's Muammar Gaddafi. Western officials fear instability in Syria and the wider Middle East if protesters oust Assad, whose family has ruled for four decades and kept Syria's frontier with the Israeli-occupied Golan Heights quiet despite its anti-Israel alliance with Iran.