Washington (AFP) - The United States expects to accept between 5,000 and 8,000 Syrian refugees in 2016, officials said.

State Department spokesman John Kirby on Monday also said 15,000 Syrian refugees have been referred to the US for resettlement by the UN refugee agency.

In December, Washington had said it had received 9,000 referrals from the UN.

It had also previously said it would admit between 1,000 to 2,000 Syrian refugees in fiscal year 2015, and increase that number by a few thousand in fiscal year 2016.

The United States has been criticized for not taking more of the estimated four million refugees fleeing the civil war that began in 2011.

Kirby argued that the US was a "leader" in terms of accepting refugees and contributing financially to resettlement efforts, but that this work was "not the metric of success here."

"And so, what we're really committed to is helping to foster the kind of political transition inside Syria, so that it is a safe environment for Syrian people to return, including the millions that are seeking refuge in Turkey right now," he added.

The US has contributed $4 billion in humanitarian aide to those affected by the Syrian violence since 2011.

UN High Commissioner for Refugees Antonio Guterres has said that the number of Syrian refugees surpassed four million in July and was expected to grow to 4.27 million by the end of the year.