ISTANBUL - The blossoming trade relationship will be the focus of a one-day trip to Turkey by Russian President Vladimir Putin, though differences between the two countries over the conflict in Syria will likely be aired.

Putin's visit to Istanbul on Monday is his first trip in two months. The unusual break in his travel schedule fed speculation that the 60-year-old Russian leader is suffering from serious back trouble or another illness. His spokesman has attributed Putin's discomfort to a pulled muscle, and the president has appeared more mobile recently.

During the talks, Turkey is likely to argue for tougher action against Syrian President Bashar Assad. The Kremlin has shown no inclination of relinquishing its support for its last Middle East ally, whom it has shielded from international sanctions and continued to provide with weapons.

Russia and China have used their veto power at the U.N. Security Council to block any U.N. sanctions on Assad's regime over its crackdown on an uprising that began in March 2011.

Moscow has also insisted that it would honor weapons contracts signed earlier with Syria for the delivery of anti-ship and air-defense missiles. Despite Western demands to halt the trade, the Kremlin has argued that the sales don't violate any international agreements.

Russia and Turkey were recently at loggerheads over Syria.

In October, Russia reacted angrily to Turkey's decision to force a Syria-bound passenger plane flying from Moscow to land in Turkey because Turkish officials said there was military equipment on board. Moscow said the plane was legally carrying radar parts for Syria.