The Russian parliament has authorised President Vladimir Putin to use military force in Syria, where Putin deployed warplanes and battle tanks earlier this month in support of the forces of President Bashar al-Assad and has called for an international coalition to battle the Islamic State.
The Russian parliament unanimously voted to grant Putin the right to deploy the country's military in Syria and carry out air strikes, a move a top Kremlin aide said related only to the air force.
Russia, which has been supporting government forces of President Bashar al-Assad in a conflict that pits him against Western-backed rebels now suddenly, finds itself in a situation where it is pitted against the Islamic State militants that both the West and Assad's forces are fighting.
The authorisation caps speedy military and diplomatic efforts by Russia in recent weeks to bolster the government of Bashar al-Assad, a long-time Moscow ally, who is locked in a bloody war against rebels at home and the Islamic State militants.
Kremlin officials said that Assad had requested Russian military support and that Russian planes would strike targets in Syria at the Syrian government's request.
A deeper engagement by Russia, however, could complicate the war in Syria despite the tacit understanding between Washington and Moscow over defence issues, including efforts to open channels to avoid possible conflicts in the multi-layered battles in Syria.
But, despite their differences over Syria, Russian President Vladimir Putin and US President Barack Obama shared a toast during a luncheon at the UN General Assembly.
Even as the United States and its NATO allies wage airstrikes against Islamic State positions in Syria, the West blames Assad's forces for crackdowns and attacks that have forced millions to flee the country - and now joining a wave of migrants and asylum seekers pouring into Europe.
''Russia will factually be the only country to carry out this operation on the legitimate basis of the request of the legitimate government of Syria,'' Dmitri S Peskov, Putin's spokesman, told journalists after the vote.
The US-led coalition, on the other hand, launched thousands of airstrikes in Syria in the past year, and even armed and trained some of the anti-Assad rebels.
Russia's authorisation to use force would force a change in tactics by Western allies even as it raised concerns of accidental conflict involving US-led coalition aircraft and Russian jet interceptors and surface-to-air missiles.
The resolution seeking authorisation came without warning in the Federation Council, Russia's higher body of parliament, where 162 senators voted unanimously in support after a closed-door discussion.
In a brief statement, the Kremlin said that Putin had requested the authorisation to use force ''on the basis of universally recognized principles and norms of international law.''
''The atmosphere was entirely one of solidarity,'' Oleg Morozov, a member of the Federation Council, said of the debate. ''There were no questions that might have influenced this atmosphere.''