Ongoing concerns about the crisis in Ukraine and nervousness ahead of policy decisions in the UK and Europe are expected to keep London stocks flat on Thursday.On the back of recent heavy falls, the FTSE 100 closed Wednesday's session at 6,636.16 - its lowest finish since April 17th - as risk appetite was dampened by weak economic data and a build-up of Russian troops along the eastern border of Ukraine.Nato has said that the recent significant increase of Russian troops near Ukraine is of "great concern" amid fears that Moscow is readying to invade. Oana Lungescu, a spokeswoman for the North Atlantic Treaty Organization, said that reports of 20,000 soldiers along the border represents "a dangerous situation".Meanwhile, with upcoming votes on interest rates at the Bank of England (BoE) and European Central Bank (ECB) injecting further uncertainty into markets on Thursday, City sources predict the UK benchmark index will pause for breath in early trading. "From a policy standpoint, I believe both [the BoE and ECB decisions] will somewhat of a non-event," said research analyst Joshua Mahony from Alpari UK. "However, it is the ECB meeting that has the potential to really move the market, with many looking to the subsequent Q&A session from Mario Draghi for potential clues to future actions."Stocks to watchRandgold Resources said it is on track to hit its production guidance for 2014 after passing more milestones in the second quarter. Gold production in the three months to 30 June was down 2% on the first quarter at 277,283 ounces but up 41% on last year. RSA returned to profit in the first six months of the year, to the tune of £69m before tax. In parallel the company announced an 82% increase in tangible equity and a return to a surplus - of £50m under IAS 19 - of its pension plans. Net written premiums were 9% lower to reach £3.9bn, but by a lesser 3% on an underlying basis. The company is targeting a restart to dividend payments alongside its 2014 year results.As it looks to reinvigorate and turn around, Aviva showed resilience in the face of a fast-shifting industry and delivered improvements in its five key metrics, increasing cash remittance, operating profits and new business, as well as cutting both costs and combined operating ratio. With challenges in the period including an overhaul of the UK annuity market, a particularly harsh winter in Canada, UK floods and a stronger pound, operating profits increased 4% to £1.05bn in the first half, a 9% increase in constant currency, with operating earnings per share up 16% and book value climbing 7%.BC