BRUSSELS, Oct 7 (Reuters) - Russia’s military build-up in Syria includes a “considerable and growing” naval presence, long-range rockets and a battalion of ground troops backed by Moscow’s most modern tanks, the U.S. ambassador to NATO said on Wednesday.

Speaking on the eve of a NATO defence ministers meeting to be dominated by Russia’s intervention in Syria’s civil war, U.S. Ambassador to NATO Douglas Lute said Moscow had managed a “quite impressive” military deployment over the past week to its Syria naval base in Tartous and its army base in Latakia.

“There is a considerable and growing Russia naval presence in the eastern Mediterranean, more than 10 ships now, which is a bit out of the ordinary,” he told a news briefing.

“The recent Russian reinforcements over the last week or so feature a battalion-size ground force ... There is artillery, there are long-range rocket capabilities, there are air defence capabilities,” Lute said.

A battalion is typically around 1,000 soldiers.

Western officials say that in strategic terms, Russia’s new air strike campaign in Syria appears designed to help reverse rebel gains increasingly endangering Syrian President Bashar al-Assad, protect Russian military assets in the country including its sole Mediterranean port, and reassert Moscow’s place as a big international power competing with the United States.

“The force that they have deployed down there is actually quite impressive for a rapid deployment of a week or so,” Lute said. “(It is) all arms, combined arms, attack aircraft, it is the attack helicopters and artillery, rocket artillery.”

Russia’s ground forces in Syria include some of its most advanced tanks, he added.

A U.S.-led coalition has been waging air strikes against Islamic State militants, Syria’s most powerful insurgent force, since last year but NATO is not directly involved.

However, Russian air space violations of NATO-ally Turkey near the border with Syria at the weekend have brought the crisis right up to the alliance’s borders. NATO called the incursions “unacceptable” and dismissed Russia’s explanation that they were a mistake caused by bad weather.

Russia’s air campaign in Syria, at a time when relations with the West are at a post-Cold War low over Ukraine, has caught Washington and its allies on the back foot and risks an incident between Russian and U.S. warplanes, now operating in the same country for the first time since World War Two.

On Wednesday, Russian and Syrian forces carried out what appeared to be the first major coordinated ground assaults on Syrian insurgents, targeting rebels in the west rather than Islamic State militants, a monitor said.

Russia says it shares the West’s aim of preventing the spread of Islamic State who have seized large expanses of Syria. But fighters on the ground and Western nations have said Russian warplanes have targeted mainly rebels who have seized areas in western Syria, and is aimed more at shoring up Assad rather than routing Islamist militants predominating to the north and east. (Reporting by Robin Emmott)