New Delhi, June 27 -- Sergei Ivanov, a former Russian defense minister once seen as a possible successor to President Vladimir Putin, has died. He was 73.

The Kremlin said Ivanov died on Friday without providing the cause of death or giving other details. Putin sent his condolences to Ivanov's family.

Putin and Ivanov knew each other since the 1970s when they both worked as young KGB officers in their hometown of Leningrad, as St. Petersburg was called during the Soviet times.

When Putin was first elected in 2000, Ivanov served as secretary of Russia's Security Council. In 2001, Putin made Ivanov his defense minister, the job he held until 2007, overseeing the second war in Chechnya that crushed the region's separatist bid.

When Putin...