LONDON (AP) -- Global stock markets tumbled again Thursday, battered by persistent worries about U.S. housing loan problems and their possible damage to the global economy.

The slides came despite moves by the U.S. Federal Reserve to add more cash to the U.S. banking system on Wednesday and action by other central banks since last week that still failed to calm investors' nerves.

In London the FTSE 100 Index dropped 3.1 percent to 5,919.60, trading below the 6,000 level for the first time since March. About 108.9 billion pounds (euro108.7 billion; US$216.9 billion) has been wiped from the value of Britain's leading stocks since trading closed last Wednesday.

France's CAC-40 declined 2.8 percent to 5,289.21 after earlier dropping to its lowest level this year, and Germany's DAX index fell 2.7 percent to 7,248.13.

"Europe has opened up with heavy losses this morning after yet more losses on Wall Street overnight," said Scott Scrase, a trader at CMC Markets. "There could be further losses to come."

In Asia, the benchmark Nikkei 225 index closed down nearly 2 percent on the Tokyo Stock Exchange after falling below the key 16,000-point mark the first time since November. South Korea's main benchmark fell 6.9 percent to its lowest finish since May, and Hong Kong's blue chip Hang Seng Index dropped 3.3 percent to its lowest close in two months.

Repercussions in global markets were bigger compared to the loss of 1.3 percent Wednesday in the U.S. -- where the loan problems erupted -- with at least three Asian markets losing more than 6 percent on the day.

That's because of uncertainty over the size of impact on corporate earnings and the regional economy, said Shinichi Ichikawa, chief strategist at Credit Suisse. He said the weakness of the dollar and the euro also fueled the concerns.

"The issue of the subprime loans is not just the problem of that sector but it also affects many related financial products, (and) the size of a possible damage or other details are not clear, and that's why investors are feeling uneasy," Ichikawa said.

On Wednesday in the U.S. the Dow Jones industrial average fell 1.29 percent to 12,861.47, closing below 13,000 for the first time since April 24. U.S. stocks appeared headed for another sharp retrenchment Thursday as fears persisted of widening problems with some mortgages and tighter access to credit.

"All of Asia and other European markets are watching the U.S. market," said James Soh, a strategist at Korea Investment & Securities Co. in Seoul. Global investors were focused in particular on the U.S. Federal Reserve, he said.

Some investors have been calling for the U.S. central bank to free up more cash by making an interest rate cut at its Sept. 18 meeting.

The Bank of Japan injected 400 billion yen (US$3.4 billion; euro2.5 billion) into money markets Thursday, the third time since last Friday it has acted in a bid to curb rises in a key overnight interest rate.

Despite the move, banking issues took a beating due to the global credit concerns.

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Associated Press Writer Mari Yamaguchi in Tokyo contributed to this report.