U.S. President Donald Trump's administration may fall short of its promise to build 450 miles of wall along the U.S. border with Mexico by the end of next year, a top official said on Tuesday.

Trump made the construction of a border wall a centerpiece of his 2016 election campaign, and has continued to focus on building a wall as he seeks re-election next year.

"Our goal at the end of 2020 was 450 miles," said Mark Morgan, acting commission for the U.S. Customs and Border Protection. "It's hard right now to be able to say whether we're still going to be able to meet that goal, but I'm confident that we're going to be close."

Morgan said that 93 miles of wall had been built so far during the Trump administration. At least 90 miles of that replaced existing structures, according to CBP figures – although Morgan said that all barriers built under Trump should be considered "new."

A U.S. federal court order handed down last week that blocks the administration from transferring 3.6 billion U.S. dollars in military construction funds to build a border wall could negatively affect the timeline if the ruling is not quickly lifted by an appeals court, Morgan said.

Trump administration officials have said for months that they aim to build 450 miles of new and replacement wall by November 2020, when the presidential election will be held.

Trump himself has been less exact. He said in April he expected his administration would build "close to 400 miles" of wall within a roughly two-year timeframe. But during a September news conference at the border in San Diego, he said the anticipation was that nearly 500 miles would be completed by the end of 2020.

The 3.6 billion U.S. dollars in military construction funds that have been blocked for use for a border wall represent roughly a third of the approximately 10 billion U.S. dollars that the Trump administration has obtained for wall construction.

A spending package passed by the House of Representatives on Tuesday would maintain funding for border barriers at 1.37 billion U.S dollars, which Morgan indicated would be used for wall construction.

The Senate is expected to take up the spending package before current funding expires at the end of the week.