"I think they finally recognize that an additional 5,000 is not a serious response," said one aide, who spoke on condition of anonymity.

The State Department official said the administration planned to increase the number of refugees it takes in from Syria and sub-Saharan Africa, particularly those affected by conflict in the Democratic Republic of Congo.

"When we talk about increasing overall numbers, we're talking about increases for people from around the world," the official said, adding: "In addition to bringing in more Syrians, which is the plan, we would like to admit more African refugees next year." The official spoke on condition of anonymity.

Since the start of the four-year-long Syrian civil war, the United States has taken in 1,500 refugees, with 300 more expected to be cleared by October.

European countries have taken in waves of migrants fleeing violence. Germany allowed 20,000 in over the weekend and is preparing for 800,000 this year.

"We are committed to increasing the number of refugees that we take and we are looking hard at the number that we specifically can manage," Kerry told reporters.

Some US lawmakers are pressing the administration to do more about the crisis.

The senior State Department official said Kerry had spoken with his German counterpart over the past 24 hours.