San Francisco: The US Department of Homeland Security is developing a plan right now for taking in at least 10,000 Syrian refugees over the next year, within existing budget constraints, Secretary Jeh Johnson told Reuters on Tuesday.

While some lawmakers have expressed concern about opening a pipeline into the United States for terrorists, the White House last week made the first specific US commitment to increase acceptance of refugees from the war-torn country.

Johnson said on Tuesday that the security review and background checks for refugees would mainly fall to Citizenship and Immigration Services (CIS) within his agency. That unit’s budget is mostly derived from fees it collects, said Johnson, who spoke to Reuters after a swearing-in ceremony for new citizens in San Francisco.

‘CIS does not depend upon, and cannot expect, appropriations from Congress,’ Johnson said. ‘The organisation has to pay for itself.’

He added: ‘Any additional undertaking has to be balanced against resource requirements, and how we are going to pay for those resources.’

White House spokesman Josh Earnest told reporters on Monday that the administration for the moment does not see the need to seek additional funding to process refugees.

‘There certainly is the potential for that in the future, but as of right now, that’s not necessary,’ Earnest said.

Since the start of the Syrian civil war in 2011, the United States has taken in 1,500 refugees, with 300 more expected to be cleared by October.

Refugee advocates and some members of Congress have said taking in an additional 10,000 refugees did not go far enough toward addressing the humanitarian crisis triggered by the war, which has prompted a massive influx of migrants from Syria and other countries into Europe.

Some congressional Republicans, including Representative Michael McCaul of Texas, who chairs the House of Representatives Homeland Security Committee, have said that allowing in Syrian refugees could serve as a pipeline for terrorists and have objected to plans to increase numbers.

Johnson said the Department of Homeland Security has significantly improved how refugees are vetted. ‘We should do and will continue to do a very thorough and careful screening of anybody,’ he said.