* Tony Tan resigns as GIC executive director and SPH chairman effective July 1
* Tan will run for president in upcoming elections (Adds quotes, background)
SINGAPORE, June 23 (Reuters) - Tony Tan, executive director at Singapore's sovereign wealth fund GIC, said on Thursday he has resigned and will run for president in an election that must be held before end-August.
Tan, a former deputy prime minister, has also resigned as chairman of Singapore Press Holdings (SPH), which controls almost all newspapers published in the city-state.
"There is no legal requirement for me to resign from GIC or SPH. However, to avoid the appearance of conflict of interest, I have decided to resign from GIC with effect from July 1," Tan said in a statement.
"I will also resign from SPH with effect from July 1 to remove any doubts about SPH's media independence," he added.
Although mostly ceremonial, Singapore's president has powers to veto senior appointments to the civil service and government-linked firms such as GIC, which manages around $250 billion, according to the Sovereign Wealth Fund Institute.
The election comes after the ruling People's Action Party (PAP) swept back to power in May general elections but with a reduced percentage of votes.
Tony Tan, 71, will likely face former ruling party parliamentarian Tan Cheng Bock, 71, who is also chairman of Chuan Hup Holdings .
Tan Kin Lian, 63, the former chief executive of NTUC Income, an insurance cooperative controlled by the government-backed trade union body, has also announced his candidacy.
Tan Kin Lian has been endorsed by members of Singapore's opposition. The PAP has yet to back any particular candidate.
Tony Tan said at a news conference: "I've made it clear that I'm not seeking the backing of any political party but obviously as a candidate I welcome support from all quarters."
Singapore's president is directly elected but the post has only been contested once -- the first time it became an elected post in 1993 -- mainly because potential candidates must meet several tough requirements.
For instance, prospective candidates must either be a former minister or top government servant. If the person comes from the private sector, he or she must have been chairman or CEO of a Singapore-based firm with a minimum paid-up capital of S$100 million ($81.1 million).
All candidates are then screened by a government committee before the election is held.
Incumbent president S.R. Nathan, 86, a former senior civil servant, has been in office for two six-year terms and was elected unopposed both times. He has not announced if he would retire or run for another term. ($1 = 1.233 Singapore Dollars) (Reporting by Kevin Lim and Walter Sim)