WASHINGTON, June 16 (Reuters) - U.S. regulators on Wednesday again delayed a decision on whether to approve an application for what would be the country"s first bitcoin exchange traded fund (ETF), filing a request for public consultation over concerns about market manipulation. The move by the U.S. Securities and Exchange Commission (SEC) on Wednesday was the second delay for the VanEck Bitcoin Trust"s proposed bitcoin ETF after an extended delay in April. Analysts say the regulator is worried it is does not have proper surveillance over crypto exchanges to ensure adequate investor protections are in place. Any adoption of a bitcoin ETF by new SEC chair Gary Gensler could be key for mainstream adoption of cryptocurrencies as it would allow financial institutions and retail traders to gain exposure without having to invest directly, they added. In its request for consultation, the SEC asked for views on the proposed Trust"s susceptibility to manipulation and its ability to prevent fraudulent acts. It also sought comment on the liquidity and transparency of the bitcoin markets and the suitability of bitcoin as an underlying asset for an ETF. Applications are reviewed within 45-day windows and the agency can take up to 240 days to make a decision. VanEck filed its ETF proposal at the end of 2020, with Cboe BZX agreeing to act as VanEck’s exchange partner earlier this year.