* FTSEurofirst 300 down 1.2 pct
* Companies with big Russia exposure hit again
* Bayer falls on UK regulatory block
* China's lower-than-expected PMI weighs on sentiment
(Adds quote, details, updates prices)
LONDON, March 24 (Reuters) - European stocks fell on Monday, trimming last week's lofty gains as concern over events in Ukraine and China's flagging manufacturing activity pegged a key index back from the top of its recent range.
Shares of companies with big exposure to Russia were under pressure as the United States began crisis talks with European allies after Ukraine announced the withdrawal of its troops from Crimea, effectively yielding the region to Moscow's forces.
Finnish tyre maker Nokian Renkaat was down 1.7 percent, Austrian lender Raiffeisen Bank International down 1.9 percent and Danish brewer Carlsberg down 1.3 percent. The three firms derive about 26 percent, 22 percent and 17 percent respectively of their revenues from Russia, according to data from MSCI.
While the developments did not mark a severe setback, confirmation that geopolitical uncertainty would continue into a fourth week was enough to see European shares retrace some of last week's gains.
The FTSEurofirst 300 gained 1.8 percent last week, buoyed by assurances from Russia that it would not intervene in the affairs of any other regions in Ukraine.
"Geopolitical tensions have eased somewhat... but the market remains susceptible to negative headlines," Atif Latif, director of trading at Guardian Stockbrokers, said, highlighting the withdrawal of Ukrainian troops from Crimea and a build-up of Russian troops on the border.
NATO's top military commander said on Sunday Russia had built up a "very sizeable" force on its border with Ukraine, and that Moscow may have a region in another ex-Soviet republic, Moldova, in its sights.
The FTSEurofirst 300 was down 1.2 percent at 1,292.26 points at 1509 GMT, bringing it back from the top end of the 125-point range it has traded in for the last five sessions.
"The equity market's long-term trend is still positive," Barclays France director Franklin Pichard said. "But in the short term, indexes could remain stuck in this consolidation zone and within tight ranges."
Shares in Bayer were among the biggest European blue-chip losers, down 3.5 percent after Britain's healthcare cost agency recommended the state health service not use the firm's new prostate cancer drug Xofigo.
Also under pressure were industrials, after China's flash Markit/HSBC Purchasing Managers' Index (PMI) fell to an eight-month low of 48.1 in March, a weaker-than-expected figure. The index has been below the 50 level since January, indicating a contraction in the sector this year.
"China's slowdown is sharper than most people had expected, which fuels worries about the impact on global growth," said Philippe de Vandiere, analyst at Altedia Investment Consulting in Paris.
"But Chinese authorities have plenty of tools to avoid a hard landing, and we know that the country's transition to an economic model more focused on consumer spending will lower its growth rate a bit, so no big concern here."
Europe bourses in 2014: http://link.reuters.com/pad95v
Asset performance in 2014: http://link.reuters.com/rav46v
Today's European research round-up
(Additional reporting by Blaise Robinson in Paris and Sudip Kar-Gupta in London; Editing by John Stonestreet)