One day after calling U.S. Secretary of State John Kerry a liar, Russian President Vladimir Putin met with President Barack Obama as part of the G-20 summit on Thursday, NBC News reported.

Putin and Obama shook hands in front of cameras in St. Petersburg at a summit which ordinarily focuses on economic issues, but the main geopolitical topic this time around remains the Syrian civil war.

Syria's Bashar al-Assad's main weapons supplier is Russia, and President Putin stated that the U.S. plans for military strikes were an equivalent to an act of "aggression" if they did not come with unanimous United Nations Security Council approval.

Tensions between the U.S. and Russia remain high, and Putin's latest jab on Wednesday against did nothing to quell that notion.

"I saw debates in Congress," Putin said at a meeting of his human rights council in the Kremlin. "A congressman asks Mr. Kerry: 'Is al Qaeda there? He says: 'No I am telling you responsibly that it is not.' Al Qaeda units are the main echelon, and thy know this. It was unpleasant and surprising for me-we talk to them, we proceed from the assumption that they are decent people. But he is lying and knows he is lying. It's sad."

To compound matters for President Obama, Brazilian President Dilma Rousseff canceled preparations for a trip to Washington, reportedly "furious" that National Security Agency had spied on her communications.

While Putin insisted that he would like to hold private talks with Obama during the summit, the U.S. President is likely to meet with leaders of France, China and Japan instead, news reports said.

This action comes a day after Senate Foreign Relations Committee voted 10-7 in favor of giving Obama authorization to launch an attack against Assad's forces. This marked the first time since a 2002 resolution that preceded the Iraq War, in which members of Congress voted to authorize military action. Expected votes in the House and the Senate are due next week.

Reports from Israel reported that the Lebanese terrorist group Hezbollah is preparing to defend Assad from an possible invasion by rebel groups, which would seek his overthrow. The group stated it will attack the Jewish State, should ensions worsen, like airstrikes aimed at the Syrian regime.