WASHINGTON — U.S. employers added a robust 288,000 jobs in April, the most in two years, evidence that the economy is picking up after a brutal winter slowed growth.

The Labor Department also said today that the unemployment rate sank to 6.3 percent, its lowest level since September 2008, from 6.7 percent in March. But the drop occurred because the number of people working or seeking work fell sharply. People aren’t counted as unemployed if they’re not looking for a job.

In addition to the strong hiring in April, employers added more jobs in February and March than previously estimated.

Employers have now added an average of 238,000 jobs the past three months, up from 167,000 in the previous three.