MOSCOW, May 22 (RIA Novosti) - At least one security guard has been killed during an armed robbery on cash couriers in downtown Moscow, Russian investigators said on Friday.

A gunman, armed with a TT pistol, fired at least four shots at a group of security guards delivering cash at about 12:30 Moscow time (08:30 GMT).

"One of the guards was injured and taken to a Moscow hospital," the Russian Investigation Department said in a statement. "The robber has been detained."

A police source earlier told RIA Novosti that a security guard had been killed in the attack, and another wounded. The robber, who was also injured in the shootout, is reported to have died on his way to hospital.

Earlier in the day, three muggers attacked a cash courier in his car in eastern Moscow. They smashed his car windows and made off with his money bag. The total amount stolen has yet to be established.

Police said the security guard had been slightly hurt in the robbery.