* Reports say leaked emails show graft by Zuma's friends
* Zuma under fire as ANC splits over leadership race
* ANC to vote on Zuma's successor in December
By Joe Brock
JOHANNESBURG, June 1 (Reuters) - Leaked documents released by the South African media on Thursday alleging improper dealings in government contracts will open President Jacob Zuma up to renewed scrutiny and may deepen divides in the ruling African National Congress.
Zuma has survived calls to resign from within the usually united ANC in recent weeks due to disputes over political appointments and his friendship with the Indian-born Gupta family, wealthy businessmen whose companies have contracts with state-owned firms.
Investigative journalists at AmaBhungane, a non-profit group that has a strong track record of exposing what it says are government corruption scandals, released some of more than 100,000 leaked emails and documents.
It says they prove Gupta-owned companies unduly influence the award of government contracts worth hundreds of millions of dollars - including the building of locomotives and pre-payments for coal deliveries before a deal was signed.
A Gupta family spokesman did not respond to questions by phone and said he may reply to emailed inquiries from Reuters later. The Gupta family and Zuma have denied wrongdoing when similar allegations have been made in the past.
Spokesmen for Zuma and the ANC did not respond. Reuters was not independently able to verify the allegations.
Zuma is due to appear in parliament at 2 p.m. (1200 GMT) to respond to questions about the presidency budget. There is no planned interaction with lawmakers but he will likely face heckling from opponents in the chamber.
"Zuma is running a criminal state and is using state institutions to enrich himself and his friends," Mmusi Maimane, leader of the opposition Democratic Alliance, told Reuters.
"These documents show once again that the ANC has embarked on a state-sponsored corruption campaign that runs deep."
The latest allegations of influence-peddling may deepen a divide in the ANC as factions battle for control ahead of a conference in December where Zuma's successor as party leader will be chosen. Zuma can remain as head of state until a 2019 election.
Zuma's camp is expected to back his ex-wife and former African Union chair Nkosazana Dlamini-Zuma, while another faction will support Deputy President Cyril Ramaphosa.
The contents of the leaked confidential government documents will likely embolden Zuma's opponents in the ANC who want to oust him or prevent his chosen successor from becoming party president in December, analysts say.
"The leaks will play into the factional battle over succession which is getting intense. The stakes are very high," said Daryl Glaser, politics professor at Johannesburg's University of Witswatersrand.
"I don't think that what comes out will be enough to result in Zuma resigning before December."
A constitutionally mandated anti-graft watchdog said in a report last year that the Guptas had undue influence over government officials and former deputy finance minister Mcebisi Jonas said he was offered a promotion by the family.
Jonas and finance minister Pravin Gordhan were removed by Zuma in a reshuffle in March.
On Wednesday, government ministers bowed to mounting pressure and told Eskom to remove its chief executive Brian Molefe, a Zuma ally, after senior politicians and the public reacted with anger at his re-appointment two weeks ago.
Molefe resigned in November last year following allegations he had links to the Gupta family. Molefe denied wrongdoing and said he resigned in the interest of good governance. (Additional reporting by Mfuneko Toyana; Editing by Alison Williams)