US stocks are starting the week with big gains after a major telecommunications deal and signs that Japan's nuclear crisis is stabilizing.

AT&T Inc. said it will buy rival T-Mobile USA for US$39 billion, creating the largest US cellphone company. The deal raised hopes that businesses are becoming more confident in the economic recovery.

The Dow Jones industrial average closed above the psychologically important 12,000 mark for the first time since the nuclear crisis in Japan began.

The Dow climbed 178 points, or 1.5 percent, to 12,037. The S&P 500 rose 19, or 1.5 percent, to 1,298. The Nasdaq composite gained 48, or 1.8 percent, to 2,692.

Five stocks rose for every one that fell on the New York Stock Exchange. Consolidated volume came to 4.6 billion shares.