Pimco, home to the world's largest bond fund run by co-founder Bill Gross, upgraded its assessment on U.S. economic growth on Wednesday, saying it now expects expansion to run between 2.5 percent and 3 percent in 2014.

In its global economic outlook, Pimco said its improved baseline expectation for real growth in the United States stems from "trends toward growth and spending in the consumer, corporate and public sectors."

In December, Pacific Investment Management Co, better known as Pimco, had said the firm expected U.S. economic growth to run between 2.25 and 2.75 percent in 2014.

"The global economy will likely experience steady, broad-based growth in 2014 thanks in no small part to the extraordinary expansion in central bank balance sheets in 2013," portfolio manager Saumil H. Parikh said in the report.

A spokeswoman said Parikh's report represents the views of Pimco, which oversaw $1.91 trillion in assets under management as of December 31.

"Rising asset prices in combination with fading near-term fiscal uncertainties will drive global aggregate demand growth forward, adding stability to what has thus far been an on-again, off-again global recovery from the financial crisis of 2008," the report said.

Pimco also upgraded its outlook on the euro zone, saying it now expects real economic growth in the region to measure between 1 percent and 1.5 percent.

"We expect the reduction in fiscal drag in the euro zone periphery will reinforce gradually improving credit conditions to drive aggregate demand growth from well below potential to up toward potential in the year ahead," Parikh said.

In December, Pimco had pegged euro zone growth at about 0.25 percent to 0.75 percent in 2014.

Pimco doesn't have as positive an outlook for Asia, where it expects Japan's growth to slow from a roaring 3 percent in 2013 to only 0.5 percent to 1 percent in 2014.

"We anticipate Japan will be the only major developed economy experiencing a slowdown this year," Parikh said. "The reduction in Japan's extraordinary fiscal stimulus of 2013, via both less growth in spending and higher tax rates, will drive the economy to contribute far less to global aggregate demand in 2014."

And China's "growth is likely to continue to slow, and our outlook is a wider range, at 6.5 percent to 7.5 percent, to reflect rising uncertainty," Parikh said. "While that is a manageable range, China's outlook poses increasing downside risk to the global outlook in 2015 and beyond. The pace of structural reforms in China appears too slow, while runaway credit creation at the local government level funded by off-balance-sheet wealth management products threatens to distract Chinese policymakers away from accelerating much-needed reforms."

He added: "Expect China to feel like a much slower growth economy in the years ahead, especially if one observes it as a commodity or capital goods exporter to the rest of the world."