(Adds details on Anglo business overhaul, production curbs from...

(Adds details on Anglo business overhaul, production curbs from paragraph three onwards)

JOHANNESBURG, July 23 (Reuters) - Anglo American's AAL.L South African iron ore unit said on Tuesday it continues to build stockpiles at its mines due to persistent rail and port constraints.

Kumba Iron Ore KIOJ.J said iron ore stockpiles at its mines swelled to 8.2 million metric tons in the first half of this year from 7.1 million during the same period last year as rail and port challenges worsen.

The persistent logistics constraints will likely weigh on parent Anglo, which is restructuring its businesses after fighting off a $49 billion attempted takeover by the world's No. 1 miner, BHP Group (BHP) .

Anglo has said it wants to retain the South African iron ore business even as it unbundles its platinum unit in the country, and also plans to divest or sell its De Beers diamond business and its Australian steelmaking coal assets.

Africa's top producer of iron ore hauls the product on an 861 km (535 mile) rail line that runs from its giant Sishen mine in South Africa's Northern Cape province to Saldanha port.

The line, managed by South Africa's state-owned Transnet "continued to be constrained by a number of derailments and equipment failures" in the first-half, said Kumba CEO Mpumi Zikalala.

The company has been forced to curb mining production and cut some jobs to save costs as it struggles to move the iron ore to ports for export to markets including China and Europe.

Kumba's headline earnings per share in the six months ended June 30 slumped 26% to 22.27 rand, hit by softer iron ore prices and the logistics challenges.

The miner declared an interim dividend of 18.77 rand per share.