Jittery Asian stocks surrendered early gains and turned lower on Monday, adding to last week's steep losses, while gold shot to new highs as investors worried about the sluggish U.S. economic outlook and Europe's festering debt crisis.

Spot gold prices hit a record $1,878.39 per ounce as the shaky global outlook prompted investors to move more money into the safe haven, while oil prices tumbled on hopes Libya may resume full output soon as a six-month civil war seemed to be nearing an end.

Japan's Nikkei 225 index was marginally lower by midday, with increasing expectations that Tokyo will intervene in forex markets to weaken the strong yen offsetting growing worries that the U.S. economy may be sliding back into a recession.

Shares elsewhere in the region as measured by the MSCI Asia Pacific ex-Japan index fell almost 1 percent after briefly edging into positive territory earlier in the session.

A similar pattern was seen in S&P 500 futures, which recoiled from early gains to slip 0.2 percent by noon, pointing to more losses in Western markets later in the day.

Given the economic hurdles faced in Europe and the United States, an upward trend is hard to sustain, said Park Yong-myung, a fund manager at Hanhwa Investment Trust Management.

Khiem Do, head of Asian multi-asset with Baring Asset Management in Hong Kong, said there would be little visibility on the direction of markets until it was clear whether the United States will slide into recession or not.

The sentiment of markets is very weak at the moment, he said.

MSCI's world stock index fell 0.3 percent, bringing its losses since late July to around 16 percent, closing in on the 20 percent decline that is often used to define a bear market.

A key event this week will be a speech by Federal Reserve Chairman Ben Bernanke on August 26 in Jackson Hole, Wyoming, during which he is expected to provide an economic outlook and hints on how policymakers plan to handle the turmoil in financial markets.

Bernanke used the same event last year to suggest the Fed could help growth by buying long-term bonds, but no major announcements are expected this time.

On Friday, U.S. stocks fell after Hewlett-Packard's weaker outlook and corporate shakeup added to uncertainty for investors after a month of bad surprises ranging from a U.S. credit rating downgrade to a sharp slowdown in world growth.

Markets will also watch data on bond buying by the European Central Bank and debt issuance by European countries such as Italy on Tuesday to see if the euro zone's debt crisis is worsening.

Also on Tuesday, a raft of preliminary manufacturing data will shed light on whether economies from China to the euro zone are continuing to lose momentum.

Brent oil futures fell 2.3 percent to $106.10 a barrel, weighed down by a firmer U.S. dollar and as the months-long conflict in oil-producing Libya appeared to enter its decisive phase, with rebel fighters streaming into the heart of Tripoli.

The dollar index, which tracks the strength of the greenback against a basket of currencies, rose 0.1 percent.

The dollar surged higher against the yen, but later pared some of its gains, with traders citing talk that the spike in the dollar was triggered by bids by a U.S. bank.

The move came as investors were increasingly on edge about the possibility that Japan may intervene to curb yen strength, in the wake of the dollar's drop down to a record low around 75.95 yen late last week.

The dollar was last flat on the day at 76.77 yen, having risen to as high as 77.23 yen earlier.

(Additional reporting by Ayai Tomisawa in Tokyo and Ju-min Park in Seoul; Editing by Kim Coghill)