Syrian President Bashar al-Assad's latest visit to Moscow has yet again pulled his Russian counterpart Vladimir Putin closer to the centre stage in the Middle East conflict, where the latter gains leverage in dictating terms on key players. Unsurprisingly, Assad's tour has angered the US.

The Obama administration, which has been leading a coalition in Syria and Iraq against Islamic State (Isis) militants for several months, has heaped scorn on the development. The White House condemned Russia's decision to accord the embattled Syrian leader a "red carpet welcome".

"We view the red carpet welcome for Assad, who has used chemical weapons against his own people, at odds with the stated goal by the Russians for a political transition in Syria," White House spokesperson Eric Schultz told reporters.

This was Assad's first overseas trip since the uprising-turned-civil-war broke out in 2011, highlighting the global isolation of the Syrian regime for years. The Syrian leader travelled to Moscow in an unannounced trip aboard a Russian military aircraft at the request of Russia, which has been dramatically snatching opportunities to play a vital role in the conflict in recent months. Assad's itinerary has reportedly been kept secret, until he returns to Damascus.

During a press briefing, US State Department spokesperson John Kirby said: "It's not surprising that Bashar Assad would travel to Moscow, given the relationship Syria has with Russia, and given the recent military activities by Russia in Syria on behalf of Bashar al-Assad."

Moscow waded itself into Syria, to shore up support for Assad, against anti-regime forces in September 2015 and has been intensifying its presence in the Middle Eastern country. Putin, who is determined to position himself as the essential power-broker in the region, has also been holding talks with other major parties including the Middle East's oil powerhouse Saudi Arabia and Turkey -- both harsh critics of the Syrian regime.

When asked about Assad's trip to Moscow, Turkish Prime Minister Ahmet Davutoglu sarcastically said: "If only he could stay in Moscow longer, to give the people of Syria some relief; in fact he should stay there so the transition can begin."

The Syrian President's surprise visit has come in the wake of the upcoming meeting between US Secretary John Kerry and his Russian equivalent, Sergei Lavrov in Vienna over the Syria situation. The Russian foreign ministry said in a statement: "The focus of attention was on the situation in Syria in regard to preparations for a meeting between foreign minister and state secretary slated for October 23 in Vienna where the heads of the foreign ministers of Saudi Arabia and Turkey are to join." This will also be the first face-to-face encounter between Kerry and Lavrov since Russia began its airstrikes in the region.