* Lawson jumps as much as 7 pct on takeover talk
* Uncertainty over BOJ action next week is rattling investors
* Financial stocks underperform on fears of deeper negative rates
By Ayai Tomisawa
TOKYO, Sept 15 (Reuters) - Japan's Nikkei share average fell to near three-week low on Thursday as uncertainty over the Bank Of Japan's policy review next week continued to take a toll on banking stocks.
On the other hand, convenience store operator Lawson Inc surged 7 percent after the company and Mitsubishi Corp said Mitsubishi was considering a takeover of Lawson, though they added that no decision had been made.
The Nikkei fell 1.5 percent to 16,359.78 in midmorning trade, the lowest since Aug. 26.
Traders said investors were nervous ahead of the BOJ's Sept. 20-21 meeting, fearing it may cut interest rates more deeply into negative territory.
"Worries that the BOJ is struggling to come up with effective policy are making investors risk averse," said Yoshinori Shigemi, global market strategist at JPMorgan Asset Management.
"Investors think that the BOJ cannot make everyone happy ... they think that there will be no monetary policy out from the meeting which will benefit every business sector in Japan."
Sources familiar with the BOJ's thinking said that it will consider making negative interest rates the centrepiece of future monetary easing by shifting its prime policy target to interest rates from base money at its review next week.
Sources said there is no consensus at this point on whether to cut rates.
Bank stocks extended this week's declines, with Mitsubishi UFJ Financial Group dropping 2.3 percent, Mizuho Financial Group shedding 1.9 percent and Sumitomo Mitsui Financial Group declining 2.1 percent.
Other financials also underperformed. Securities stocks Nomura Holdings and Daiwa Securities Group each tumbled 3.6 percent.
Insurers were battered, with Dai-ichi Life Insurance dived 4.3 percent and Sompo Japan Nipponkoa Holdings shed 2.1 percent.
The broader Topix dropped 1.4 percent to 1,296.99, with all of its 33 subsectors in negative territory.
The JPX-Nikkei Index 400 declined 1.4 percent to 11,634.65. (Editing by Kim Coghill)