“There are more than 2,000 militants in Syria from the former Soviet Union. So instead of waiting for them to return back home we should help President al-Assad fight them there, in Syria,” he added, according to a Kremlin transcript of the interview, which was broadcast in the US on Sunday night.
Mr Putin is due to address the United Nations General Assembly for the first time in 10 years on Monday, ahead of a bilateral meeting with Barack Obama.
It will be the first talks between the two leaders in two years. Mr Putin is expected to use both events to call for an international alliance against Islamic State that would include the Syrian regime.
A baby is rescued after an airstrike by forces loyal to Assad in Damascus
Mr Obama and other western leaders have ruled out cooperation with Mr Assad, saying his forces are responsible for the vast majority of civilian deaths and that most refugees arriving in Europe are fleeing government violence. Mr Putin described that view as “anti-Syrian propaganda.”
In an earlier released extract of the interview Mr Putin confirmed that one objective was to "save" Mr Assad's regime, which suffered a series of battlefield setbacks earlier this year.
President Putin: Russian ground troops will not take part in battlefield operations in Syria ?for now?
The comments follow a flurry of Russian military and diplomatic activity across the Middle East that has been described by western diplomats as an attempt to overcome nearly two years of international isolation following Russia’s annexation of Crimea and backing of a separatist uprising in east Ukraine.
Challenged on his government’s policy on
Ukraine, Mr Putin attacked the United States for organising what he called a “coup” to overthrow Viktor Yanukovych, the former president of Ukraine in February 2014.
“We know the ways the assistance was provided, we know how much they paid them, we know which territories and countries hosted trainings and how it was done, we know who the instructors were. We know everything,” he said. He did not provide details.
A satellite image showing MI-24 attack helicopters at Bassel Al Assad Air Base in Syria
He denied using military force to attempt to restore what he sees as “legitimate power” in Ukraine. Western governments accuse him of sending troops and weaponry to support the separatist side in the 17-month war in Ukraine's Donbass region.
In other comments, Mr Putin said he still stands by his famous 2005 remark that the collapse of the Soviet Union was the "greatest geopolitical catastrophe of the twentieth century," and said the Russian diaspora abroad remained a major issue.
“Do you think it is normal that 25 million people, Russian people, suddenly found themselves abroad? The Russians have turned out to be the largest divided nation in the world nowadays.” he said.
"The Soviet Union has traditionally been called Russia, the Soviet Russia, and it was the great Russia. They used to live in one country and suddenly found themselves abroad. Can you imagine how many problems came out?"
Protecting the post-Soviet Russian diaspora was one justification the Kremlin gave for annexing Crimea in March 2014.
Asked about Republican presidential candidate Marco Rubio's characterisation of him as a gangster, saying his background as a spy precluded involvement in organised crime.
“How can I be a gangster, if I worked for the KGB? It is absolutely ridiculous,” he said.
Mr Rubio said last month that Mr Putin is "basically an organized crime figure who controls a government."
