European stock markets dropped on Wednesday when banking share prices tumbled in reaction to the eurozone\'s deepening debt crisis. London\'s FTSE 100 index of top shares fell 0.58 percent to 5,988.58 points approaching midday trade, Frankfurt\'s DAX 30 slipped 0.23 percent to 7,422.38 points and in Paris the CAC 40 index lost 0.36 percent to 3,964.88. The Stoxx 50 index of leading eurozone companies shed 0.63 percent to 2,832.99 points. \"And so the European vicious circle continues with the spotlight focusing on Portugal once again,\" said Simon Denham of trading group Capital Spreads. \"There seems to be no end in sight for the peripheral eurozone states as once one problem seems to have been temporarily resolved, the same problem in another country rears its ugly head.\" Moody\'s Investors Service late on Tuesday slashed its credit rating on indebted eurozone struggler Portugal, bailed out earlier this year, by four notches to Ba2 from Baa1, warning it could be lowered further. The agency said the downgrade reflects \"the growing risk that Portugal will require a second round of official financing before it can return to the private market (to raise financing).\" Greek Foreign Minister Stavros Lambridinis attacked on Wednesday what he termed the \"madness\" of ratings agencies in the European debt crisis, saying they exacerbated an already difficult situation. On Monday, Standard & Poor\'s warned that current proposals for a second Greek bailout could constitute an effective default. Banking shares meanwhile led the losers on Wednesday, with Royal Bank of Scotland down 3.04 percent to 38 pence, UniCredit diving 4.73 percent to 1.432 euros and Credit Agricole shedding 3.39 percent to 9.994 euros. US stock markets ended mostly lower on Tuesday, giving up a bit of the ground they gained during a strong five-day rally last week. The Dow Jones Industrial Average fell 0.10 percent to close at 12,569.87 points. US markets had closed on Monday because of the July 4 Independence Day holiday. Before the holiday, Wall Street enjoyed its strongest week in two years, with the Dow surging 5.4 percent in five days. Japan\'s Nikkei index closed above 10,000 points on Wednesday to mark its highest finish since March 11 when an earthquake and tsunami devastated the northeast coast and triggered a nuclear crisis.