A big fall in sales of Nokia's basic phones overshadowed a stronger performance from its Lumia smartphones in the first quarter.
The company said it expected operating margins to deteriorate, sending its shares down as much as 11% in earlier trade.
The Finnish mobile phone maker also reported an unexpected fall in sales at its previously upbeat equipment venture Nokia Siemens Networks.
Nokia, which has fallen behind Samsung and Apple in the smartphone race, said it sold 5.6 million units of Lumia handsets in the first quarter, up from 4.4 million in the previous quarter and in line with expectations.
But overall net sales fell 20% to €5.9 billion from a year earlier, while phone volumes tumbled 30% on the previous quarter.
It forecast that margins in its devices and services business would be "approximately negative 2%" in the second quarter, down from a positive 0.1% in the first quarter.
The company's first-quarter underlying loss, which excludes special items, decreased to two cent from eight cent a year earlier. Markets had expected a four cent loss.