MOSCOW - Russia is denying any role in the poisoning of a British couple who British authorities insist are the latest victims of Novichok — allegedly a Russian-made military-grade nerve agent first implicated in an assassination attempt on a former Russian spy and his daughter on British soil last March.

The initial attack left former Russian agent Sergei Skripal and his daughter, Yulia, hospitalized in serious condition for several weeks before their ultimate recovery. The incident set off an international crisis that Kremlin officials seemed less than eager to repeat in the face of renewed allegations.

"Of course we're concerned that these substances have been used repeatedly in Europe," said Kremlin spokesman Dmitry Peskov. "However, on the other hand, we have no information about which substances were used or how they were used."

British nationals Dawn Sturgess, 44, and Charlie Rowley, 45, both fell ill in Amesbury — less than 16 kilometers (10 miles) from Salisbury — showing symptoms British medical personnel have described as consistent with those in the Skripals' poisoning.

Russia has angrily denied any involvement in the incidents, arguing Moscow never possessed Novichok and had nothing to gain politically from an attack on a former double agent seemingly in retirement.

Yet, in the wake of the Amesbury incident, Russian officials have concentrated their frustration on British authorities' continued refusal to allow Russian investigators to participate in a joint investigation.

"It is regrettable that U.K. officials try to link a second poisoning with Russia without having produced any credible results of the investigation of the first one," the Russian Embassy in Britain said in a statement. "Instead of genuine cooperation, London is doing everything possible to muddy the waters, to confuse and frighten its own citizens."

A police officer stands at a cordon around the ben FILE - A police officer stands at a cordon around the bench where former Russian intelligence agent Sergei Skripal and his daughter Yulia were found after they were poisoned, in Salisbury, Britain, March 11, 2018. FILE - A police officer stands at a cordon around the bench where former Russian intelligence agent Sergei Skripal and his daughter Yulia were found after they were poisoned, in Salisbury, Britain, March 11, 2018.

"There is a need for thorough and professional work, and the efforts of British security services will not be enough," added Vladimir Shamanov, chairman of the defense committee in Russia's lower house of parliament, the Duma.

"Russia should be involved, among others," he added.

The revival of the Novichok issue presents an additional challenge to East-West relations just days ahead of a July 16 summit in Helsinki between U.S. President Donald Trump and Russian counterpart Vladimir Putin that both sides say is much needed to thaw existing tensions.

British Prime Minister Theresa May is all but certain to raise the subject when Trump visits London for talks prior to the Helsinki summit.

In the wake of the March attack against the Skripals, the U.S. joined with Britain in marshaling the largest mass expulsion of Russian diplomats by Western allies since the days of the Cold War.

At the time, British authorities argued, and U.S. officials concurred, that it was "highly likely" Moscow was either behind the attack or had lost control of its chemical weapons stores.

Renewed focus on the poisonings serves as an unwelcome distraction from Russia's continued hosting of World Cup 2018, which visiting soccer fans have overwhelmingly lauded as a success.

The event has helped burnish Russia's international image following years in which the Kremlin argues it has been unfairly demonized over everything from its policies in Ukraine and Syria to cyber-meddling in elections and what Washington has described as general "malign activities."

Speaking at a meeting with leaders of the world governing body FIFA in Moscow on Friday, Putin praised the tournament and world soccer fans for helping to destroy "so many stereotypes about Russia."

"People have seen that Russia is a hospitable country, a friendly one for those who come here," said Putin.

FILE - Sergei Zheleznyak, deputy speaker of the Ru FILE - Sergei Zheleznyak, deputy speaker of the Russian parliament's lower house, speaks to reporters in Moscow, March 18, 2014. FILE - Sergei Zheleznyak, deputy speaker of the Russian parliament's lower house, speaks to reporters in Moscow, March 18, 2014.

Yet Sergei Zheleznyak, deputy speaker of the Duma, argued it was Russia's very success as World Cup host that explained the sudden return of the Novichok scandal to world headlines.

"A huge number of British fans, despite the warnings from their government, came to support their team. Their impressions are just destroying everything British propaganda built over the past few years," said Zhelezhnyak. "To break up this flow of really positive emotions that the British fans are sharing, they had to put something like this in the mass media."

While British officials and the royal family have boycotted the games in protest against the Skripal poisonings, the controversy over Novichok wasn't the only source of tension between London and Moscow.

Depending on the outcome of their World Cup matches Saturday, Russia and England could square off in the semifinals.