1GENEVA (Reuters) - Bahrain must rein in its security forces after allegations they had killed protesters and attacked medical workers, UN High Commissioner for Human Rights Navi Pillay said on Thursday. Pillay voiced alarm at what she called the illegal "military takeover of hospitals" in the kingdom, where Bahraini forces used tanks and helicopters on Wednesday to drive protesters off the streets. "There are reports of arbitrary arrests, killings, beatings of protesters and of medical personnel, and of the takeover of hospitals and medical centres by various security forces," she said in a statement. "This is shocking and illegal conduct." The International Committee of the Red Cross (ICRC) also voiced alarm at the escalation in violence which it said had led to more deaths and scores of injured in recent days. "All people arrested and detained must at all times be treated humanely and held in decent conditions." Pillay, a former UN war crimes judge, said those who carried out such acts, even under orders, could be held criminally liable. Meanwhile, the leader of Bahrain's largest opposition group has urged Saudi Arabia to withdraw its forces and called for a UN inquiry into a crackdown on mainly Shia protesters that has raised tensions in the oil-exporting region. Bahrain arrested 7 opposition leaders on Thursday, a day after its forces moved in to end weeks of pro-democracy protests that have sucked in troops from its fellow Sunni-ruled neighbour and prompted the king to declare martial law. "The military should withdraw from Bahrain, the military of Saudi Arabia, and this is a call to the Saudi king," Sheikh Salman, head of Wefaq, told Al Jazeera TV. "We call for an investigation by the UN into what has happened from Feb 14 up to now. If protesters were in the wrong, then they should be held to account." Three protesters died in the crackdown but so did three policemen mown down by demonstrators in fast-moving cars. The crackdown has drawn sympathy protests from Shias across the Gulf Arab region, including the world's top oil Saudi Arabia, and Iran has complained to the United Nations. Iran, which supports Shia groups in Iraq and Lebanon, asked countries in the region to join it in urging Saudi Arabia to withdraw troops from the Gulf Arab island state. "How could one accept a government to invite foreign military forces to suppress its own citizens?" Iran's Foreign Minister Ali Akbar Salehi said in a letter to UN Secretary General Ban Ki-moon, also addressed to the Arab League. Bahraini state TV called the detainees leaders of "civil strife" and said they had been communicating with foreign countries and inciting murder and destruction of properties. Among those detained overnight were Haq leader Hassan Mushaima and Wafa leader Abdel Wahhab Hussein, who had led calls for the overthrow of the royal family, Wefaq officials said. More moderate Wefaq had limited its demands to wide-ranging political and constitutional reform. Also arrested was Ibrahim Sharif, head of the secular leftist party Waad that signed up to the same demands as Wefaq. "Two of the thugs climbed over the fence to get in our yard, one went over and pointed a gun in Ibrahim's face and the other went to our garage to let everyone else in," Farida Ismail, Sharif's wife, told Reuters by telephone.