The world's top brewer Anheuser-Busch InBev on Thursday posted underwhelming results for last year, as it closes in on completing a mega merger with rival SABMiller.

The Belgian-Brazilian brewer announced in November it would take over British SABMiller for $121 billion -- the third largest acquisition in history -- that would make it a juggernaut, brewing three times as much beer as its nearest rival.

The company hopes to complete the tie-up by the end of 2016 and said on Thursday it was on track to do so.

AB InBev said net profit fell by 3.95 percent in 2015 to 8.5 billion dollars, slightly lower than forecasts by analysts.

Operating profit, a closely watched statistic by investors, rose 6.6 percent to $4.31 billion when analysts were pencilling in 9.2 percent.

AB InBev sees the buyout of SABMiller as a key way to counterweight falling beer demand in big markets by building its presence in growing markets such as Africa.

AB InBev said problems persisted in once-shining markets in China and Brazil last year, putting even more pressure to finish the SABMiller deal.

The company added that a downward trend in the US was turning however, where beer-drinking levels have been on a long-term slump as consumers move to craft beer, wine and other spirits.

Worldwide AB InBev beer sales by volume fell by 0.1 percent in 2015, the company said.