U.S. immigration officials detained more than 5,000 migrants from Ukraine at the nation’s land, sea and air borders in March, with a significant increase in those seeking refuge at the U.S.-Mexico boundary, adding to the record influx of newcomers from Latin America and the Caribbean this year, according to U.S. Customs and Border Protection figures released Monday. The tally — up from fewer than 1,150 the month before — marks the first official accounting of Ukrainians seeking refuge at the ports and borders since Russia’s invasion began Feb. 24. Many, if not most, Ukrainians have been released into the United...