MOSCOW — GRU isn't as well-known a baleful acronym as KGB or FSB. But Russia's military intelligence service is attracting increasing attention as allegations mount of devious and deadly operations on and off the field of battle.

The latest charge came Wednesday, when Britain identified two suspects in this year's nerve-agent poisonings as GRU agents .

An overview of the GRU:

THE AGENCY

Formally named the Main Directorate of the General Staff of the Armed Forces, the agency is almost universally referred to by its former acronym GRU.

It is the most shadowy of Russia's secret services. When its previous director Igor Sergun died in 2016, the Kremlin announcement was so terse that it gave neither the date, cause or place of death.

The agency has an apparently broad mandate. According to the Defense Ministry website, it is tasked not only with "ensuring conditions conducive to the successful implementation of the Russian Federation's defense and security policy" but with providing officials intelligence " that they need to make decisions in the political, economic, defense, scientific, technical and environmental areas."

ALLEGATIONS

Britain claims that two GRU agents carried out this spring's attack with the nerve agent Novichok on Sergei Skripal, a former GRU officer who became a British double agent, and his daughter. Both survived the poisoning in the city of Salisbury, but three months later two area residents were sickened by the same nerve agent, one of them fatally — it is believed they found the discarded bottle that had carried the Skripals' poison.

This week's claim came less than two months after the U.S. indicted 12 alleged GRU agents for hacking into the Hillary Clinton presidential campaign and the Democratic Party and releasing tens of thousands of private communications, part of a sweeping conspiracy by the Kremlin to meddle in the 2016 U.S. election.

Also this year, the investigative group Bellingcat reported that a GRU officer was in charge of operations in eastern Ukraine, where Russia-backed separatists were fighting Ukrainian forces, in July 2014 when a Malaysian passenger airliner was shot down, killing all 298 people aboard. International investigators say the plane was shot down by a mobile missile launcher brought in from Russia. The GRU officer named by Bellingcat reportedly was responsible for weapons transfers.

Russia's RBC news service reported this year that the GRU oversees Russian mercenaries in Syria, fighting there as a so-called shadow army.

Russian authorities generally deny allegations against the GRU and refuse to discuss its activities. They said they didn't recognize the suspects Britain named Wednesday in the Salisbury poisoning.

OTHER AGENCIES

The GRU is one arm of Russia's extensive security and intelligence apparatus, which also includes the Foreign Intelligence Service, known as the SVR, and the Federal Security Service, or FSB, which conducts domestic intelligence and counterintelligence. The SVR and FSB were spun off from the KGB after the collapse of the Soviet Union. A former KGB agent, Vladimir Putin ran the FSB before ascending to the presidency.

And as president, Putin names the top brass in the GRU. Of all the agencies, the FSB looms largest in Russians' minds because it hunts domestic threats. The GRU, created under Soviet founder Vladimir Lenin, has a more ruthless reputation, but focuses its energies on foreign threats.

The agencies' operations appear to both compete and cooperate.

Pavel Felgenhauer, an independent Moscow-based military analyst, told The Associated Press that if "the SVR runs into military intelligence, they have to share it with the GRU; that means they try not to run into military intelligence and tell their agents not to report anything military even if they know it. The other way around, military or GRU assets are asked never to report anything political."

But in the case of the alleged U.S. election-related hacking, he said, "I believe that was an inter-service operation, because it's not military but they gained some kind of hacking access and then they shared it with the FSB and the SVR."