PARIS, Mar. 25 (Reuters) - President Emmanuel Macron said on Monday that the gunmen who killed 137 people in a concert hall outside Moscow were part of an Islamic State branch that was behind foiled attempts to attack France over the past few months.

This explains why the French government on Sunday increased the country's security alert to its highest level, Macron and Prime Minister Gabriel Attal said. More soldiers will be put on standby and ready to patrol sensitive sites, including schools.

Islamic State claimed responsibility for Friday's Moscow attack.

Russia, which has challenged assertions by the United States that the Islamic State militant group orchestrated the mass shooting in Moscow, continued on Monday to suggest Ukraine was to blame. Macron said this was "cynical and counterproductive".

"This attack was claimed by Islamic State," Macron said, "and the information available to us, to our (intelligence) services as well as to our main partners, indicates indeed that it was an entity of the Islamic State which instigated and carried out this attack.

"This specific group ... had over the past months carried out several (attack) attempts on our soil," he added. Attal later said these included a foiled planned attack on the city of Strasbourg, in eastern France.

"The claim of responsibility for the (Moscow) attack by a branch of Islamic State that planned attacks in European countries including France prompted us to increase the Vigipirate (security threat assessmment) to its highest level," Attal said, speaking from a Paris train station.

"We will deploy exceptional means everywhere on (French) territory," he said.

Some 3,000 soldiers are currently part of the "Sentinelle" operation that patrols sites such as railway stations, places of worship and schools and theatres. Another 4,000 will be put on standby, Attal said.

France has thwarted two would-be attacks since the start of the year, he said.

France has been hit by a series of Islamist attacks over the past decade, the worst of which, in 2015, targeted the Bataclan concert hall and cafes and bars in Paris - which some Parisians said helped them understand why security would now be beefed up.

"It (the Moscow concert hall attack) brings to mind the Bataclan years, so yes, it's something that has left a mark in us forever," said IT worker Raffele Alegretti.

Macron, who was speaking as he arrived for a visit in French Guiana, also said France had offered to increase cooperation with Russian intelligence services over the concert hall attack "so that we continue to fight effectively against these groups which are targeting several countries".

Russian President Vladimir Putin has not publicly mentioned Islamic State in connection with the attackers, who he said had been trying to escape to Ukraine. Russia has been at war with Ukraine since it invaded its neighbour in February 2022.

Putin said some people on "the Ukrainian side" had been prepared to spirit the gunmen across the border. Ukraine has denied any role in the attack and President Volodymyr Zelenskiy has accused Putin of seeking to divert blame for not securing Russia against such an attack by mentioning Ukraine.

Photo from Reuters