Security around top government officials was tightened yesterday following Wednesday's arson attack by right-of-abode seekers at Immigration Tower. Police, who arrested nine more suspects yesterday - some of them still in hospital - said all the demonstrators involved could be prosecuted. The total number of arrests now stands at 15. Immigration chiefs promised to review safety measures after meeting staff representatives, who demanded their colleagues be equipped with defensive weapons such as pepper spray, shields and batons. Nineteen of the 50 people injured during the attack remained in hospital yesterday. Seven were in critical condition, including two immigration officers. The injuries occurred at about 6pm when abode-seekers allegedly splashed paint thinner around a 200-square-foot reception room packed with 50 people and set light to it. Immigration officers had been preparing to clear them as the office closed. Security at Immigration Tower was stepped up with checks on people entering the building and no bottles of liquid, lighters or weapons allowed on the 13th floor - where the attack took place - or the 14th floor - which has taken over some of the 13th floor's duties. The first-floor lobby was closed to all except government staff, who had their identities checked. At least five police protection unit officers were seen escorting Director of Immigration Ambrose Lee Siu-kwong yesterday and his office was closed to the public. Secretary for Security Regina Ip Lau Suk-yee said she had not received threats from abode-seekers, and had confidence in the ability of the police to uphold law and order. Central's district commander, Acting Chief Superintendent Chan Kit-chu, said patrols had been stepped up around the Central Government Offices, where top officials work, and at other key points in the district. Those arrested yesterday were seven men and two women, aged between 17 and 35. Three of them were still receiving treatment in a hospital custodial ward yesterday. Together with the four men and two women arrested on Wednesday, they were being detained for questioning. Senior Superintendent Wong Fook-chuen said police would interview all 23 right-of-abode seekers involved in the incident, which was classified as arson, and would prosecute all of them if there was sufficient evidence. The attack took place after a four-hour stand-off following repeated attempts by the abode-seekers to get Hong Kong Identity Cards from immigration officials on the 13th floor of Immigration Tower. A representative of the abode-seekers who visited some of the suspects yesterday said the protesters had warned the officers they would commit suicide if they were removed. 'The immigration officers knew they would commit suicide,' she said. 'They should have stopped them rather than trying to clear them away.' While one of the abode-seekers had a knife, the representative said she wanted to use it to cut herself and not to attack anyone. Human Rights Monitor described the attack as 'barbaric' but urged the public to distinguish between peaceful abode claimants and violent ones. The Director of Immigration rejected suggestions the attack revealed lax security. 'We can't treat all protesters as thieves or else we would suppress their right to express their opinions,' Mr Lee said. Those who did not have grounds to stay would be deported, he said.