He was quoted by the Interfax news agency as saying that the drills were "also a response to the United States sanctions".
Russia's Ministry of Defence broadcast images on Tuesday of columns of tanks, armoured vehicles and warships on the move, and combat helicopters and fighter aircraft taking off.
A subsequent report from the Mint Press News further revealed that the drill will see huge action consisting of 300,000 troops, close to 40,000 military vehicles, a thousand aircraft, a couple of Russian naval fleets, and the entire airborne units coming from China.
Asked on Tuesday if the USA was anxious about a possible military alliance between Russian Federation and China, Defence Secretary Jim Mattis told Pentagon reporters he thought "that nations act out of their interests".
At the event on Tuesday, Xi said that China and Russian Federation would work together to maintain stability and peace in the world. The event, called Vostok or East 18, began as President Putin met President Xi of China. "Beijing and Moscow have to show Washington that they have an unbreakable strategic partnership".
Joint military drills are not uncommon but are rarely seen on such a large scale.
They involve 1,000 Russian Federation aircraft and 36,000 tanks.
"They feel they need to embrace to deal with the increasingly high pressure and containment from the USA", said Yue Gang, a military expert and retired Chinese army colonel.
Putin said Moscow has a "trusting relationship" with Beijing "in politics, security, and defense".
China's participation will enhance its counterattack abilities and reinforce ties with Russia, Chinese government officials said Tuesday.
The weeklong exercises reprise massive Soviet war games that took place at the height of the Cold War.
The Vostok 2018 exercise by the Russian military is witnessing its biggest military drill by the country in 37 years.
He said that an increasingly unpredictable geopolitical climate made partnership between Russian Federation and China particularly important.
"They demonstrate the seriousness of our intentions", General Ivashov said.
The drills are being held in Russia's Eastern and Central military districts, which encompass more than half of the country's territory. If we recall the "Zapad 2017", simultaneously with this event Russian Federation conducted its exercises coordinated with the "Zapad" on its territory.
The military exercises come at a time of escalating tensions between Moscow and the West over accusations of Russian interference in western affairs and ongoing conflicts in Ukraine and Syria.