International Business Machines last night reported a bigger-than-expected decline in revenue for the first time in five quarters due to weak demand in its IT services business.

This could be a sign that the company's turnaround could take longer than expected. 

IBM's revenue has now fallen for 20 quarters in a row.

With demand for its legacy hardware and software businesses stagnating, IBM has been shifting towards cloud-based services, security software, data analytics and artificial intelligence such as its supercomputer Watson.

This once defeated human contestants in the quiz show Jeopardy. 

These "strategic imperatives", spread across IBM's various businesses, continued to grow in the first quarter.

But they failed to offset weakness in the company's core operations, especially at the technology services and cloud platforms business. 

IBM could not close some large deals in that business, which is its largest, while a couple of large clients took their operations in-house, the company's chief financial officer Martin Schroeter said on a conference call. 

As a result, IBM's overall revenue decline increased to 2.8% in the first quarter from 1.3% in the fourth quarter, and widely missed analysts' expectation of a 1.6% drop.

IBM's revenue of $18.16 billion in the first quarter missed analysts' estimate of $18.39 billion, according to Thomson Reuters I/B/E/S. 

Revenue in the technology services and cloud platforms business dropped 2.5% to $8.2 billion. The business accounted for about 45% of total revenue. 

The company said gross profit margin fell in all five of its reporting units. Overall adjusted gross margin of 44.5% missed analysts' estimates of 47.7%. 

However, "strategic imperatives" revenue growth accelerated to 12% in the first quarter from 11% in the fourth. 

Revenue from "strategic imperatives" was $7.8 billion in the latest quarter, accounting for 42% of total revenue, up from 37% a year earlier.