Washington (CNN) The Trump administration has built 100 miles of new wall along the US-Mexico border -- the majority of which is replacing previous construction -- acting Homeland Security Secretary Chad Wolf announced in Arizona on Friday, as the administration touts its record ahead of the presidential election.

Against the backdrop of a section of wall, Wolf called the 100-mile mark "a milestone achievement."

But the 100 miles are only a portion of the administration's goal to build 450 miles by the end of this year and the majority replaces wall that was already in place. As of December 6, around 90 miles of barriers that had been constructed replaced old, dilapidated designs, according to US Customs and Border Protection. The agency has not provided updated figures.

Three years into his presidency, President Donald Trump has faced a host of legal challenges over his border wall and his attempt to shore up the effort with additional funds from other government accounts. As the election year ramps up, his key campaign promise is likely to take on new urgency.

"This is a milestone achievement for the President, the department and more importantly, for our country, including communities like Yuma," Wolf said Friday.

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