WASHINGTON, June 23 (Reuters) - U.S. Vice President Kamala Harris will visit the U.S.-Mexico border on Friday for the first time since taking a lead role in immigration issues, her office said, bowing to pressure that she make the high-profile trip. Harris will travel to El Paso, Texas, on Friday and will be accompanied by Homeland Security Secretary Alejandro Mayorkas, Harris spokeswoman Symone Sanders said. President Joe Biden assigned Harris the task of addressing the root causes of migration of thousands of people from El Salvador, Guatemala and Honduras who cross the U.S. border from Mexico. She visited Mexico and Guatemala earlier this month. Republicans have assailed Harris for not having already visited the border. Harris had said she would do so eventually. Former President Donald Trump, who plans a border visit on June 30, said in a statement: "If (Texas) Governor (Greg) Abbott and I weren’t going there next week, she would have never gone!" Biden, a Democrat, has moved to reverse many of the restrictive immigration policies of Trump, a Republican he defeated in a November election. At the same time Biden has left in place a border policy known as Title 42, expelling in five months more than 400,000 migrants detained at or near the border, including many Central American families and asylum seekers sent back to Mexico. Publicly, the Biden administration insists the order remains necessary to limit the spread of the coronavirus, although it has yet to provide scientific data to support that rationale and many public health experts have opposed it. Nearly 3,300 migrants stranded in Mexico since January due to a U.S. border policy have been kidnapped, raped, trafficked or assaulted, according to a report by a human rights group released on Tuesday. The report, by New York-based Human Rights First, documents cases of migrants and asylum seekers stuck in Mexico since Biden took office on Jan. 20. The number of cases has jumped in recent weeks from roughly 500 such incidents logged in April to 3,300 by mid-June.