Operating profit of German auto giant Volkswagen increased by nearly 22 percent in the first quarter, thanks to record sales of luxury brands of Audi and Porsche, said the company on Tuesday. Compared with the same period of previous year, Volkswagen's operating profit rose by 21.8 percent to about 2.9 billion euros (about 4 billion U.S. dollars) in the first three months in 2014. Its sales revenue grew by 2.7 percent to 47.8 billion euros. Its luxury brand Audi contributed the most to its total gains with an operating profit of 1.3 billion euros in the first quarter. During the same period, Sports car Porsche recorded an operating profit of 698 million euros, 125 million euros more than in the previous year. "The Volkswagen Group has established a strong position in recent years. Our good start to the current fiscal year is an additional proof of this," said Volkswagen Chief Executive Martin Winterkorn in a statement. The Wolfsburg-based company aimed to deliver over 10 million vehicles in 2014, following a delivery of more than 9.7 million units last year and 4 years ahead of its initial plan. On Tuesday, Volkswagen said it expected 2014 sales revenue to "move within a range of 3 percent around the prior-year figure", and forecasted an operating return on sales of between 5.5 percent and 6.5 percent in 2014. It said weak currencies of key emerging economies pushed up prices and put pressures on demand in the first quarter. Over the whole year of 2014, challenges would come from difficult market environment and fierce competition, as well as interest rate and exchange rate volatility and fluctuations in raw materiel prices.