MOSCOW (AP) — President Vladimir Putin on Tuesday watched Russia's biggest military maneuvers since Soviet times, involving 160,000 troops and about 5,000 tanks across Siberia and the far eastern region in a massive show of the nation's resurgent military might.

Dozens of Russia's Pacific Fleet ships and 130 combat aircraft also took part in the exercise, which began on Friday and continue through this week. Putin watched some of the drills on Sakhalin Island in the Pacific, where thousands of troops were ferried and airlifted from the mainland.

Russia's Deputy Defense Minister Anatoly Antonov assured foreign military attaches on Monday that the exercise was part of regular combat training and wasn't directed against any particular nation, though some analysts believe the show of force was aimed at China and Japan.

Konstantin Sivkov, a retired officer of the Russian military's General Staff, told the daily Nezavisimaya Gazeta that the Sakhalin part of the maneuvers was intended to simulate a response to a hypothetical attack by Japanese and U.S. forces.

Russia and Japan have a dispute over a group of Pacific islands, which Russia calls the Kurils and Japan calls the Northern Territories.

The islands off the northeastern tip of Japan's Hokkaido Island were seized by Soviet troops in the closing days of World War II. They are surrounded by rich fishing grounds and are believed to have offshore oil and natural gas reserves and other mineral resources.

Antonov said that Russia had warned its neighbors about the exercise before it started, and provided particularly detailed information to China in line with an agreement that envisages a mutual exchange of data about military activities along the 4,300-kilometer (2,700-mile) border.

The two Cold war-era rivals have forged what they described as a "strategic partnership" after the 1991 Soviet collapse, developing close political, economic and military ties in a shared aspiration to counter U.S. power around the world.

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Russia has supplied sophisticated weapons to China, and the neighbors have conducted joint military drills, most recently a naval exercise in the Sea of Japan earlier this month.

But despite close economic ties and military cooperation, many in Russia have felt increasingly uneasy about the growing might of its giant eastern neighbor.

Some fear that Russia's continuing population decline and a relative weakness of its conventional forces compared to the Chinese People's Liberation Army could one day tempt China to grab some territory.

Russia and China had territorial disputes for centuries. Relations between Communist China and the Soviet Union ruptured in the 1960s, and the two giants fought a brief border conflict in 1969.

Moscow and Beijing signed a new border treaty in 2004, which saw Russia yielding control over several islands in the Amur River. Some in Russia's sparsely populated far east feared that the concessions could tease China's appetite.

Alexander Khramchikhin, an independent Moscow-based military analyst, said that the massive exercise held in the areas along the border with China was clearly aimed at Beijing.

"It's quite obvious that the land part of the exercise is directed at China, while the sea and island part of it is aimed at Japan," he said.

Khramchikhin, who recently posted an article painting a grim picture of Russia being quickly routed in a surprise Chinese attack, said that the war games were intended to discourage China from harboring expansionist plots.

"China may now think that Russia has finally become more aware of what could happen," he said, describing the exercise as a sobering signal.

The maneuvers are part of recent efforts to boost the military's mobility and combat readiness after years of post-Soviet decline, but they have far exceeded previous drills in both numbers and territorial scope.

As part of the war games held across several time zones, some army units deployed to areas thousands of kilometers away from their bases. Paratroopers were flown across Russia in long-range transport planes, and some units were ferried to Sakhalin under escort of navy ships and fighter jets.

A decade of post-Soviet economic meltdown has badly crippled Russia's military capability, grounding jets and leaving navy ships rusting in harbors for lack of funds to conduct training. Massive corruption and vicious bullying of young conscripts by older soldiers have eroded morale and encouraged widespread draft-dodging.

The weakness of the once-proud military was shown in two separatist wars in Chechnya when Russian troops suffered heavy losses at the hands of lightly armed rebels.

The Russian military won a quick victory in a war with Georgia's small military in August 2008, but the five-day conflict also revealed that the military had trouble quickly deploying its forces to the area. The shortage of precision weapons and modern communications were also apparent.

The Kremlin responded by launching a military reform intended to turn the bloated military into a more modern and agile force.

The government also has unveiled an ambitious arms modernization program that envisages spending over 20 trillion rubles (over $615 billion) on new weapons through 2020.

Some military analysts cautioned, however, that the rearmament effort was badly planned and might not be sufficient to reverse the military's decline. "This program is clearly insufficient," Khramchikhin said.