* FTSE 100 down 0.7 pct, near lowest since late April
* Ex-dividends take up to 14 points off FTSE 100
* Ukraine/Russia tensions hit global equity markets
* Ofwat warning weighs on Utd Utilities
By Sudip Kar-Gupta
LONDON, Aug 6 Britain's top equity index fell on Wednesday to around its lowest level in more than three months, as mounting concerns over the situation in Ukraine and Russia weighed on stock markets.
United Utilities also underperformed, slipping back by 1.7 percent after British water regulator Ofwat said it had written to United Utilities and other water companies to get them to lower customers' costs.
The blue-chip FTSE 100 index was down by 0.7 percent, or 42.86 points, at 6,639.62 points in early session trading, hovering near its lowest level since late April.
The FTSE's decline matched similar pullbacks in Europe, as equities fell after reports that Russian troops were buildng up at the eastern Ukrainian border, where pro-Moscow rebels are in conflict with the Ukrainian government - ratcheting up the tension in the region.
Russian President Vladimir Putin has also ordered his government to prepare retaliatory measures against the latest round of Western sanctions, Russian news agencies reported on Tuesday.
"As the tensions mount, we'll see more of a correction on the equity markets. The mentality now is not to buy on dips but to sell on rallies," said Securequity sales trader Jawaid Afsar.
The FTSE also experienced a pullback due to technical reasons, as several companies - including oil major BP, bank Barclays and drinks group SAB Miller - went "ex-dividend", meaning they were trading without the attraction of their latest dividend payout.
Beaufort Securities sales trader Basil Petrides saw the FTSE making little progress in the near term.
"In the absence of any reason to go higher, the market will follow the path of least resistance, and go down," he said. (Editing by Hugh Lawson)