July 6 (Reuters) - Vietnam shares retreated on Wednesday after hitting an eight-year high in the previous session as investors booked profits, while Thailand was marginally down, led by losses in energy and financial stocks.

But activity across much of the region was subdued as most markets were closed for Eid al Fitr.

Asian share markets turned tail as fears over instability in the European Union returned with a vengeance, sending the pound fo three-decade lows and hammering risky assets of all stripes.

MSCI's broadest index of Asia-Pacific shares outside Japan was down 1.7 percent at 0420 GMT.

Concerns that central banks might not be able to soften this latest blow to global growth hit oil prices hard. U.S. crude was down 31 cents at $46.29 a barrel, after a 5 percent fall in the previous session as U.S. investors digested news of an OPEC increase in production after the July 4 holiday.

Investors rushed to safe-haven assets such as sovereign debt and gold. Gold climbed to its highest in more than two years early on Wednesday.

Vietnam's benchmark stock index was down 0.2 percent after seven sessions of gains. Healthcare and energy stocks led the decline, with Petrovietnam Gas Joint Stock Corp and Dhg Pharmaceutical Joint-Stock Co down 0.8 percent and 1.5 percent, respectively.

Thai shares were headed for their second straight loss after five sessions of gains. Investors are trading to "take profit" for a while, said an analyst with KGI Securities Thailand, adding that the "Thai market will perform above 1,450 points".

Indorama Ventures Pcl rose 2.6 percent, while PTT PCL fell nearly 1 percent. Singapore, Malaysia, Indonesia and Philippine stock markets were closed on Wednesday for Eid al Fitr.