The share placement is not related to any specific events, a UBS spokesman said.
UBS is taking this action now in order to take advantage of current market opportunities, he said.
The Swiss bank, one of the world's hardest-hit major banks in the global financial crisis, said on Thursday it was offering about 293.3 million new shares at a price of 13.00 Swiss francs per share, a 6.9 percent discount to Thursday's closing price of 13.97. It also said it would post a second-quarter net loss.
(Reporting by Jason Rhodes; Editing by Hans Peters)
($1=1.099 Swiss Franc)