The Taoiseach has said the EU will stand behind Britain after a nerve agent attack on a former Russian spy and his daughter in the UK.

The British Prime Minister Theresa May has said it is “highly likely” Russia was behind the attack – and warned of potential sanctions against the Eastern power if it does not provide answers by midnight tonight.

Sergei Skripal and his daughter Yulia both remain in a critical condition after being found unconscious on a bench in Salisbury nine days ago.

In a series of tweets this evening, the Russian embassy in London again protested the Kremlin’s innocence and insisted it would not respond to the ultimatum until it “receives samples of the chemical substance to which the UK investigators are referring.”

It called for the UK to “comply with the Chemical Weapons Convention” and agree to a joint investigation and warned that any threat of “punitive” measures against Russia “will meet with a response.”

International support

Leo Varadkar was speaking in Washington DC not long after a phone call on the issue between US President Donald Trump and Theresa May.

President Trump said America is with Britain 'all the way', and that Russia must provide “unambiguous answers.”

The Taoiseach said they would also have the support of Ireland and the EU:

The Taoiseach says he expects the EU to support Britain if they call for any aid after the poisoning in #salisbury pic.twitter.com/mDz2V2YzYb

— Sean Defoe (@SeanDefoe) March 13, 2018

“No matter who did it and no matter where it occurred, it is something that the Irish government is appalled at and roundly condemns,” he said.

“In terms of what response we have seen from the UK; even thought the UK is leaving the EU we still want to have a very deep security partnership with the UK.

“They are still our neighbour and we still want to be friends of theirs so certainly the EU will respond, I think, favourably to any call for support from Britain.”

Investigation

It comes as British detectives say it's still too early to say whether Sergei Skripal and his daughter Yulia were poisoned at their home.

The UK head of counter-terrorism policing Neil Basu speaking at Scotland Yard, 13-03-2018. Image: Kirsty O'Connor/PA Wire/PA Images

UK counter-terrorism chief Neil Basu told reporters that 38 people - including the Skripals and the first police officer to respond – have been treated by medics since the incident nine days ago:

“Of those, 34 have been assessed,” he said. “And – I make this clear – have been discharged from hospital.”

“Three remain in hospital and that is Sergei, Yulia and Nick.

“One person continues to be assessed as an outpatient, but is not showing signs at this time.”

Solidarity

Earlier, the Tánaiste expressed his "grave concern" over the nerve agent attack on a former Russian spy and his daughter in the UK.

Simon Coveney said Ireland condemns the attack and joins many other states in supporting the UKs efforts to ensure a thorough investigation into the incident.

We stand in solidarity with our closest neighbour and friend in the face of a disturbing and shocking chemical nerve agent attack in U.K. pic.twitter.com/PbtblZOT3T

— Simon Coveney (@simoncoveney) March 13, 2018

He said Ireland “condemns this cowardly attack which has taken place on our neighbour’s soil.”

“The use of chemical weapons, including the use of any toxic weapons, is unacceptable and abhorrent,” he said.

“The incident in Salisbury represents a disturbing violation of international law and goes against norms which have long been established.”

“We offer our full support and solidarity to the UK and to the Organisation for the Prohibition of Chemical Weapons (OPCW) in their efforts to seek answers and take appropriate action for this indiscriminate and reckless act.”

"A reckless and despicable act": PM's statement to Parliament on the use of a nerve agent in Salisbury. https://t.co/mYtcjCjUPQ

— UK Prime Minister (@10DowningStreet) March 12, 2018

Yesterday, British Prime Minister Theresa May said it was “highly likely” Russia was behind the attack - a claim Russian officials have denied.

She said the Skiprals had been hit with a ‘Novichok’ military-grade nerve agent which was developed by Russia from the 1970s onward.

She demanded answers from the Russian government by midnight tonight.

"Either this was a direct act by the Russian State against our country, or the Russian government lost control of this potentially catastrophically damaging nerve agent and allowed it to get into the hands of others," she said.

Russian Foreign Minister Sergey Lavrov, 13-03-2018. Image: AP Photo/Alexander Zemlianichenko, Pool

Earlier Moscow again insisted it was not behind the poisoning.

The country's Foreign Minister Sergei Lavrov criticised the UK for refusing to let Russian investigators test samples recovered from Salisbury:

“As soon as the rumours first started being spread by practically every member of the British Government that the substance Skripal was poisoned with came from the Russian Federation, we immediately made an official request to gain access to this substance so that our experts could carry out an analysis.

Public health

Meanwhile, health officials in the UK have insisted that public in Salisbury is safe – despite a warning from the doctor who developed the nerve agent used in the attack.

On Sunday, the health watchdog advised anyone who was in the pub or restaurant visited by the Skripals to wash clothing and items such as watches, phones and spectacles.

Dr Vil Mirzayanov, a chemist who ran the lab that developed Novichok agents, has warned that it is the “same as nerve gas but 10 times, at least 10 times, more powerful."

He said it was designed to do "irreparable" damage to the human body, adding that people exposed to even tiny traces of the agent could be in danger of developing symptoms in years to come.

He described "headaches, difficulty thinking, and also co-ordination (issues), a lot of problems."

When asked about the advice given by Public Health England, including washing clothes and wiping down belongings, he said: "Sure it's useful, but not enough, absolutely not."

He said that anyone who may have been exposed should be offered "permanent medical surveillance."

More than two decades ago, Dr Mirzayanov became so concerned about Novichok agents that he blew the whistle and fled to America, where he campaigned to get all chemical weapons banned.

Additional reporting from Sean Defoe ...