How can I block select in Konsole?

In terminal emulators like GNOME terminal, I can hold the control key and use my mouse to select a block of text. Doing the same in Konsole has no effect -- the mouse simply selects one character after another, to the end of each line, wrapping around, as if I were using GNOME terminal and selecting text without holding the control key. How can I block select text in Konsole?