Washington, Jun 7 (IANS): US border agents made more than 50,000 arrests in May for the third month in a row, the Department of Homeland Security (DHS) said.

The DHS revealed on Wednesday that it took 51,912 migrants into custody in May, nearly three times the number detained in May 2017, a period when illegal immigration plunged following President Donald Trump's inauguration, The Washington Post reported.

Arrests at the border this year have jumped to their highest levels since Trump took office.

Homeland Security spokesman Tyler Houlton said in statement on Wednesday the administration's crackdown needed more time to work.

"These numbers show that while the Trump administration is restoring the rule of law, it will take a sustained effort and continuous commitment of resources over many months to disrupt cartels, smugglers, and nefarious actors," Houlton said.

"No one expects to reverse years of political inaction overnight or in a month."

Eager to campaign on his ­border security agenda ahead of November's midterm elections, Trump has told aides that curbing illegal immigration is crucial to the Republican Pasrty's success.

He cited the issue as one of his key achievements in a tweet Monday marking the 500th day of his presidency.

The vast majority of immigrants continue to come across the Rio Grande Valley of South Texas, but so far this year a greater portion have been taken into custody in southern Arizona, suggesting that migration flows may be shifting west, The Washington Post quoted the DHS as saying.

In the Border Patrol's Tucson sector, the number of underage migrants detained increased 42 per cent since last September.

In the Yuma sector, the increase is 110 per cent.

Border arrests had reached an all-time high of 1.6 million in 2000, according to DHS records.