At least one person has been killed and five wounded in a shooting at the headquarters of Russia's Federal Security Service (FSB) in central Moscow, Russian media say.
A gunman who opened fire with an automatic weapon at the entrance of the building was killed by an armed officer, Interfax news agency reports.
Security forces cordoned off the area and moved bystanders into buildings.
The shooting came hours after President Putin's annual press conference.
Details of the incident, which began shortly after 18:00 (15:00 GMT), remain unclear.
The FSB denied earlier reports suggesting there were three gunmen in the attack on its headquarters. The unconfirmed reports said two had been killed in the lobby while the third ran off to a nearby building where he was later killed in a shootout with police.
Among the injured were two seriously hurt officers, the Health Ministry told Russian media. Shortly afterwards, the intelligence agency itself confirmed the death of one FSB officer - though it is not clear if he is one of the two reported injured in the earlier report.
Russian investigators have opened criminal proceedings into the attempted murder of law enforcement officers.
They are looking into whether the attack was timed to coincide with Vladimir Putin's four-hour press conference, which ended during the afternoon.
At the scene
Will Vernon, BBC News, Moscow
The area around the FSB's two main buildings in central Moscow has been completely sealed off with large numbers of police and special forces - some armed with assault rifles - in the area.
Eyewitness Vladimir Adyasov told the BBC that he was in the vicinity of the FSB's main building on Lubyanka Square when he heard loud bangs. Mr Adyasov said he initially thought it was fireworks, but quickly realised that it was gunfire. Police officers shouted for people to flee, he added.
Videos on social media appear to show the attacker firing an assault rifle indiscriminately at the heavily-guarded building.
The attack took place on the eve of security services day - a special holiday for security staff - in Russia, and Mr Putin was addressing a meeting at the time to mark the occasion.
"We must not reduce the intensity of your work... and above all it applies to counter-terrorism," Mr Putin said, a short distance away from the attack in Moscow.
"Terrorism is an insidious and dangerous enemy, and the fight against it must continue systematically and decisively... with an emphasis on the prevention of terrorism, on preventive, offensive operations."
Some footage posted on social media appeared to capture the sound of gunshots in the area of the attack, while other video showed armed men running away from the FSB headquarters on Lubyanka Square.
Five ambulances were also seen leaving the scene.
Civilians run from shooter, as police run toward shooter. Say what you will about the Russian cops, but this is bravery on display right here. pic.twitter.com/BjevbawFGR— Kevin Rothrock, Mr. (@KevinRothrock) December 19, 2019
"I saw a member of the traffic police running down the road, hiding behind vehicles," one eyewitness told Reuters news agency.