Twenty-one people have received some form of treatment in connection with the attempted assassination of a former Russian spy and his daughter with a nerve agent in England, though only three remain in a hospital, a police official told Britain’s Sky News on Thursday.

The three still hospitalized are former Russian spy Sergei Skripall; his daughter, Yulia; and Detective Sgt. Nick Bailey, said Kier Pritchard, temporary chief constable of Wiltshire police.

Regarding the others, Pritchard told Sky News they’ve been “through the hospital treatment process, there have been blood tests and they’re having treatment in terms of support and advice.”

UK Home Secretary Amber Rudd condemned the attempted assassination of a former Russian spy and his daughter in England as “cruel” and “brazen” on Thursday, amid growing suspicions that Moscow may have been involved.

Police confirmed Wednesday that a nerve agent was used in the attack in the southern English city of Salisbury on Sergei Skripal and his daughter, Yulia, who remain in a critical but stable condition.

Western intelligence views Russia as a leading suspect based on previous attacks using a similar substance and method, a Western intelligence official told CNN. The official cautioned that it is still early in the investigation.

In a statement to members of Parliament on Thursday, Rudd refused to be drawn on who might have been responsible.

“The use of a nerve agent on UK soil is a brazen and reckless act — this was attempted murder in the most cruel and public way,” Rudd said.

“People are right to want to know who to hold to account but if we are to be rigorous in this investigation we must avoid speculation and allow the police to carry on their investigation.”

Rudd said the UK government was committed to “doing whatever we can to bring the perpetrators to justice” and would “act without hesitation as the facts become clearer.”

Skripal, 66, and Yulia, 33, were found slumped on a bench near a shopping center in Salisbury on Sunday. A police officer who helped them was also exposed to the nerve agent but his condition has improved. The officer was identified as Detective Sgt. Nick Bailey, according to Wiltshire Police spokeswoman Emma Morton.

Earlier Thursday, Rudd said that Skripal and his daughter were in a “very serious condition” but that the policeman was “talking and engaging.”

Police: Pair ‘deliberately targeted’

In a statement on Wednesday evening Mark Rowley, the head of the counter-terrorism division at London’s Metropolitan police, declared a “major incident” and said hundreds of police officers, forensic experts and government chemical analysts were involved in the inquiry.

Rowley said the attack was being treated as attempted murder, and that Skripal and his daughter were deliberately targeted.

If a Moscow link were proved, it would plunge relations between the West and Russia to a new low, and would call into question the British government’s ability to protect residents of the UK at home. Rowley said officers from Wiltshire police, the local force, were providing support to the sick officer and his family.

Sally Davies, the Chief Medical Officer for England, said the evidence did not suggest any wider danger to the public.

Police say they know the nerve agent used in the attack, but have declined to say what it was nor how they suspect it was administered. They called on anyone who visited the area on Sunday, including a branch of the Zizzi restaurant chain or the nearby Bishop’s Mill pub, to come forward with any information that might help them piece together what happened.

Russian slams UK reaction

The Russian embassy in London told reporters it had not received substantive details about the case, which it said was “rather worrying.”

A spokesman described comments by UK Foreign Secretary Boris Johnson, who vowed a “robust response” in the event that state involvement was proved, as “strongly anti-Russian.” He described the comments as an attempt to politicize the affair, and attacked the media for aiding the government’s efforts.

“The parliamentary debate as well as the Government stance are a testament of London’s growing unpredictability as a partner in international relations, whose policy towards Russia is inconsistent and looks rather miscalculated, not least in the eyes of the Russian public” the press officer added.

Skripal is believed to have lived in the UK since he was released from a Russian jail in 2010. He was convicted in Russia of spying for Britain before he was granted refuge in the UK after a high-profile spy swap in 2010 between the United States and Russia.

His daughter Yulia is thought to be one of the few members of the former spy’s immediate family still alive after his wife and son died in recent years.

Local convenience store manager Ebru Ozturk, who saw Skripal at his shop just days before the incident on Sunday, told CNN that he was a “kind customer” who would usually come in once a week and buy Polish-smoked bacon and scratch-and-win lottery cards.

“He is (a) regular customer, he is so kind and he seems to me an educated person. Very polite,” said Ozturk. “I don’t talk too much to the customers, but he was, you know, one of the very kind customers.”

‘Outrageous affront’

The executive director of the Europe-wide police agency Europol, Rob Wainwright, described the use of a nerve agent to attack a former Russian spy in the UK as an “outrageous affront to our security in Europe and our way of life,” but added that people should “exercise caution before jumping to any conclusions.”

However, he said, “there are not 101 likely offenders,” apparently a reference to the difficulty in producing nerve agent, which would limit the number of suspects with the ability to carry out the attack.

Nerve agents are rarely used outside the battlefield and require considerable expertise to develop. Exposure to potent doses can result in death.

Sarin was used in the 1995 attack on the Tokyo subway, carried out by the Aum Shinrikyo doomsday cult, which killed 13 people and injured 5,500 others. Another nerve agent, VX, was used to kill Kim Jong Nam, the half brother of North Korean leader Kim Jong Un, at Kuala Lumpur international airport in February 2017.

In his comments to parliament, Johnson said the Salisbury chase had “echoes” of the plight of former Russian spy Alexander Litvinenko, who died a slow death after drinking tea laced with highly radioactive polonium-210 in 2006 in a hotel in London.

A detailed UK inquiry later concluded that Russian President Vladimir Putin probably approved the operation by Russian agents to kill Litvinenko. The Russian Foreign Ministry dismissed the inquiry as politically motivated.