FRANKFURT (Reuters) - Deutsche Bank posted a loss in the second quarter, it disclosed on Wednesday, its first in four years after setting aside 1.3 billion euros ($1.41 billion) as a provision for a protracted investor lawsuit over its Postbank acquisition.

The bank's net loss attributable to shareholders was 143 million euros in the quarter. That compares with a profit of 763 million euros a year earlier, and was better than analyst expectations for a loss of around 280 million euros.

The loss at Germany's largest lender broke a profit streak after 15 consecutive quarters in the black, in a setback for the bank's turnaround under CEO Christian Sewing.

The bank also increased its forecast for provisions for credit losses for the full year.

Deutsche Bank executives nevertheless said the bank would meet its targets.

The bank is "well on track towards meeting our 2025 goals and our distribution commitments to shareholders", Sewing said.

($1 = 0.9222 euros)