Turkey's investment grade hangs in balance as post-coup purges deepen

(Repeats Thursday item)

* Purges raise concern about institutional weakening

* Moody's has Turkey on review for possible downgrade

* Junk status could see billions of dollars leave

* Brokerage, central bank hit by post-coup crackdown

By Asli Kandemir

ISTANBUL, July 28 (Reuters) - A crackdown in Turkey after a failed coup could further weaken its institutions and threaten its investment grade status, investors fear, as dismissals and detentions stretch from the judiciary into the private sector and even the central bank.

Turkey has suspended, detained or put under investigation more than 60,000 soldiers, judges, teachers, journalists and others suspected of ties to the network of U.S.-based cleric Fethullah Gulen, whom it blames for the July 15-16 coup attempt.

What began as a purge in the security services and judiciary has spread to commercial firms and financial institutions.

The head of research at brokerage AK Investment had his licence revoked on Tuesday over a report to investors analysing the coup plot, while the chief of Turkey's biggest petrochemicals firm Petkim was detained in connection with the events, the state-run Anadolu news agency said.

Turkish Airlines, arguably the country's most recognised brand, has fired 211 staff over alleged links to Gulen's religious movement, while a source at the central bank said purges of junior officials had also started there.

"It's certainly fair to say that foreign investors are concerned about the extent to which the purges will impact stability over the near to medium term, and what the impact on business confidence and investment propensity will be," said Manik Narain, a London-based strategist at UBS.

Turkish officials dismiss suggestions that the crackdown is too heavy-handed, pointing out that never in Turkey's history have its own warplanes been used to bomb parliament as they were during the abortive coup, and that many of the more than 240 people killed were civilians.

But in investment banks and Western capitals, many fear the purges are being used by President Tayyip Erdogan to tighten his grip and erode the already fragile independence of institutions including the courts and the media.

Moody's said on July 18 it was putting Turkey's credit rating on review for a possible downgrade to junk status, citing, among other things, the medium-term impact of the failed coup on the country's policy-making institutions and on economic growth.

Fitch has also said any downgrade decision will depend on the extent to which the government's reaction deepens political divisions and weakens institutional independence.