The iShares FTSE NAREIT Mortgage REITs ( REM) was among Tuesday's worst performers, as holding Luminent Mortgage ( LUM) stoked investors' concerns about the weakening credit market.

Luminent, in an announcement before the opening bell, said it has canceled filing its second-quarter earnings report and called off its conference call, scheduled for Thursday morning. The company also suspended its 32-cent dividend just a week after assuring investors that the payout was "secure." UBS, JMP Securities, Friedman Billings, and Keefe Bruyette all cut their ratings for the stock.

Luminent, which was recently diving more than 80% to 85 cents, is only the most recent mortgage-related name to lose nearly all of its value. Last week, American Home Mortgage, another holding of the iShares FTSE NAREIT Mortgage REITs, slid more than 93% after the company slashed 90% of its workforce and filed for bankruptcy protection. The ETF was dropping $1.15, or 3.6%, to $31.22.

Exchange-traded funds tracking Asian markets were also sliding, after several indices in Hong Kong and Japan lost ground overnight. Tokyo's Topix Index slipped 0.5%, the Nikkei 500 Index gave back 0.4%, and Hong Kong's Hang Sang gave back 0.1%.

The iShares MSCI Taiwan Index ( EWT) was lower by 29 cents, or 1.8%, to $15.77. The SPDR S&P China ( GXC) slipped $1.20, or 1.7%, to $68.10. The iShares FTSE/Xinhua China 25 Index ( FXI) sank $1.66, or 1.3%, to $129.53. The SPDR S&P Emerging Asia Pacific ( GMF) was easing by 62 cents, or 0.8%, to $74.

The Broadband HOLDRs ( BDH) was also among the worst losers, following a ruling against Qualcomm ( QCOM), banning imports of 3G phones that infringe on Broadcom ( BRCM) patents. Both stocks were losing 2.5%.

The ETF was down 42 cents, or 2.8%, to $14.77.

On the other hand, ETFs related to regional banks were among the best performers. Among individual names, Washington Mutual ( WM), Colonial Bancgroup ( CNB) and SunTrust Banks ( STI) were all gaining 1.5% or more.

The KBW Regional Banking ( KRE) ETF was higher by $1.11, or 2.7%, to $43. The iShares Dow Jones U.S. Regional Banks ( IAT) added 91 cents, or 2%, to $46.54.

Meanwhile, increases in shares of Lehman Brothers ( LEH), NYSE Euronext ( NYX) and Goldman Sachs ( GS) bolstered the iShares Dow Jones U.S. Brokers-Dealers ( IAI), which was adding 2% to $50.71.