Russian President Vladimir Putin said Monday that his country has not ruled out joining air strikes against Islamic State in Iraq and Syria [ISIS] but would not send ground troops into combat.

After his first meeting with U.S. President Barack Obama in nearly a year, the Kremlin chief said any Russian action in Syria will be in accordance with international law.

Asked if Russian aircraft could join the strikes against ISIS, Putin said, "We are thinking about it, and we don't exclude anything."

Putin said he and Obama discussed the U.S.-led coalition's action against ISIS. He did not mention Russian behaviour in backing rebels in Ukraine or its takeover of Crimea, which was at the top of Obama's agenda.

The Russian leader said the talks were "very constructive, business-like and frank."

Obama, Putin spar at UN

The U.S. and Russian presidents held the meeting on the sidelines of a United Nations summit in New York. 

Earlier on Monday, Obama and Putin sparred at the UN over what to do about the conflict in Syria.

The U.S. has no desire to return to the Cold War, Obama told the United Nations General Assembly.  

But he differed dramatically with Putin over strategies for Syria. As well, he said the world cannot stand by while Russia violates Ukraine's integrity and sovereignty.

If there are no consequences for Russia's annexation of Crimea, it could happen to any other country in the United Nations, he said.

Putin spoke later Monday morning, saying it would be a "huge mistake" not to co-operate with the Syrian regime of President Bashar al-Assad in the fight against extremists such as ISIS.

He urged the creation of a broad anti-terror coalition that would include the Syrian government troops.

Putin criticized the West for arming "moderate" rebels in Syria, saying they later come to join the Islamic State terror group.

Putin meets Cuban leader

Putin also met with Cuban President Raul Castro on the sidelines of the assembly and was expected to meet with Iranian President Hassan Rouhani as well.

For his part, Obama called Assad a tyrant "who drops barrel bombs to massacre innocent children."

In a speech that stressed tools such as sanctions and the benefits of negotiation, Obama also said he leads the most powerful military force the world has ever known and won't hesitate to use it in the defence of his country or its allies.

Obama said Russia's state-controlled media depict recent events in Ukraine as an example of a resurgent Russia. He said that view is shared by many U.S. politicians who think the world is in a new Cold War.

But Obama said that's not true: Ukrainians are more interested than ever in aligning with the West.

UN General Assembly

President Barack Obama called Syrian President Bashar al-Assad a tyrant 'who drops barrel bombs to massacre innocent children.' (Richard Drew/Associated Press)

Obama said the U.S. doesn't want to isolate Russia. Rather, he wants Russia to engage diplomatically and resolve the crisis in a way that lets Ukraine determine its own future.

"We the nations of the world cannot return to the old ways of conflict and coercion …" he said. "We all have a stake in each other's success."

In stressing the benefits of co-operation, Obama pointed to Iran and this year's deal on limiting that country's nuclear program.

"We and our partners — including Russia and China — stuck together in complex negotiations that yielded an agreement …," he said.

"We want a strong Russia that's invested in working with us to strengthen the international system as a whole."

Despite little sign of a breakthrough on Syria or Ukraine, U.S. officials insisted it was still worthwhile for the leaders to meet — something that has happened rarely since Obama vowed to isolate Putin in retaliation for Russia's provocations in Ukraine.

"The president believed it would be irresponsible to let this occasion in which the two leaders would be in the same city pass without trying to test to see whether progress could be made on these newly intractable crises," Samantha Power, the U.S. ambassador to the United Nations, said Sunday on ABC's This Week.

Russian President Vladimir Putin

Russian President Vladimir Putin said it would be a 'huge mistake' not to co-operate with the Syrian regime of President Bashar al-Assad in the fight against extremists. (Reuters)

Ahead of his UN visit, Putin deployed more weapons and troops to Syria. The Kremlin has also intensified its diplomatic efforts in recent months, launching a dialogue with Saudi Arabia, which is firmly bent on unseating Assad, and the Syrian opposition, in a renewed attempt to try to negotiate a political compromise.

"There is no other solution to the Syrian crisis than strengthening the effective government structures and rendering them help in fighting terrorism," Putin said in an interview with CBS' 60 Minutes on Sunday. 

Support for Assad

In another development, Iraq's military said Sunday it will begin sharing "security and intelligence" information with Syria, Russia and Iran to help combat ISIS. The move could further complicate U.S. efforts to battle the extremists without working with Damascus and its allies.

Russia has shown no indication that it would dump its support for Assad, whom it has shielded from UN sanctions and continued to provide with weapons throughout the nation's more than four-year civil war.

Putin's calls for strengthening Assad's military come amid striking troubles for Obama's plan to train and arm moderate rebels to fight the Islamic State in Syria. A $500 million U.S. Pentagon training program has resulted in just a handful of fighters to bolster airstrikes from a U.S.-led coalition.

The U.S. has agreed to talk with Russia about "deconflicting" their military action in Syria. U.S. Defence Secretary Ash Carter spoke to his Russian counterpart about Syria earlier this month, the first military-to-military conversation in more than a year.

Strained relationship

Obama and Putin have long had a strained relationship and their body language in face-to-face meetings is always closely scrutinized for signs of tension. Their last formal meeting was in June 2013, though they've had a number of conversations on the sidelines of international summits, including in China last November.

The Ukraine crisis drove U.S.-Russian relations to post-Cold War lows. Russia annexed Crimea from Ukraine in 2014 and a pro-Russian armed insurgency continues in eastern Ukraine, with Kyiv and NATO accusing Moscow of backing and supplying it.

A shaky peace deal for Ukraine was brokered in February by France and Germany, and Russia doesn't want the United States to become engaged in those talks. Another four-way meeting of leaders of Russia, Ukraine, France and Germany is set to take place in Paris this weekend.

Corrections

  • An earlier version of this story referred incorrectly to King Abdullah of Saudi Arabia as a speaker. In fact, the speaker was King Abdullah of Jordan. The king of Saudi Arabia is Salman. His predecessor, also named Abdullah, died in January.
    Sep 28, 2015 12:23 PM ET
With files from CBC News