Finnish telecom equipment giant Nokia's net profit fell by 29 percent in 2015, to 2.45 billion euros ($2.8 billion) ahead of acquiring its French-American rival Alcatel-Lucent, the company said on Thursday.

The drop was due to the 2014 results including 5.4 billion euros Nokia gained from selling its unprofitable handset unit to Microsoft.

But the company said operating profit grew last year by 20 percent and its net revenue by six percent.

Nokia has just gone through two and half years of radical transformation. In 2013 it bought 50 percent of its network activities from Germany's Siemens, in 2014 it divested its mobile phone business where it had been the world's number one brand, and in 2015 it sold its mapping unit Here and took control of Alcatel-Lucent.

Net profit from its "continuing activities" after the divestments and before its acquisition of Alcatel-Lucent was finalised last month, fell by 56 percent last year, to 1.19 billion euros, the company said.

Total revenue went up by 6 percent, to 12.5 billion euros.

The company hailed in a statement a "continuation of strong operational performance in Nokia Networks and solid growth in Nokia Technologies", its intellectual property unit.

But chief executive Rajeev Suri warned that Nokia saw a rough start of the year ahead.

"We do expect some market headwinds in 2016 as 4G/LTE rollouts in China and some other markets start to slow.

"The first quarter, in particular, looks quite challenging as customers assess their capex (capital expenditure) plans in light of increasing macro-economic uncertainty," he said in the statement.