* European stocks dip with Ukraine worries to the fore

* Investors await German sentiment survey

* Euro dips towards nine-month low vs dollar

* Brent crude falls below $104 a barrel

By Nigel Stephenson

LONDON, Aug 12 (Reuters) - European shares fell on Tuesday, throwing a rally in the U.S. and Asia into reverse, and the euro dipped towards nine-month lows against the dollar as reports a Russian aid convoy was heading to Ukraine ratcheted up tension between Kiev and Moscow.

Investors were waiting for a closely watched gauge of German economic sentiment, which some analysts expected will reflect the impact on the euro zone's powerhouse of Western sanctions imposed on Russia over the Ukraine crisis. The ZEW indicator is due at 0900 GMT.

"We are looking for a hard drop in the index as geopolitics is taking a toll. This comes before second-quarter GDP data on Thursday and this may form a picture that there are cracks in the euro zone recovery," said Commerzbank strategist Rainer Guntermann.

The FTSEurofirst 300 index fell 0.2 percent at 1,320.14 points, giving up a 1.3 percent gain on Monday.

The euro was down 0.2 percent at $1.3366, heading towards nine-month lows hit last week.

"If the ZEW collapses, concerns about Russia will become more intense," said Lutz Karpowitz, currency strategist at Commerzbank.

"That means the euro will not merely suffer as a result of a lack of momentum from other data today, but in the long run it will simply become more difficult for the euro if the European economy is unable to take off."

Russian shares traded mixed after strong gains on Monday. The dollar-denominated RTS index was flat while the rouble-based MICEX rose 0.5 percent. The rouble was 0.41 percent weaker against the dollar at 36.07

Moscow said a convoy of 280 trucks carrying humanitarian aid set off for Ukraine, a day after the head of NATO warned against using offers of help as a pretext for invasion.

Investors are also concerned about events in Iraq, where the president named a new prime minister on Monday to replace Nuri al-Maliki and the United States has bombed Islamic State insurgents who have marched through the north and the west of the country since June.

However, the price of oil fell on Tuesday, with Brent dropping more than $1 to below $104 a barrel. The political crisis has brought militia and special forces on to the streets of Baghdad, but it was not expected to disrupt crude supplies.

Things had looked brighter in Asia.

MSCI's broadest index of Asia-Pacific shares outside Japan rose 0.4 percent after Monday's 1.5 percent jump. In Tokyo, the Nikkei stock index firmed 0.2 percent.