Asian currencies were hit by record-high oil prices and a softer yen on Tuesday, heading back towards the lows of last week which had prompted suspected central bank intervention.
After early gains proved unconvincing, the yen softened to 111 per dollar.
Regional currencies, which weakened against the dollar through July, were pulled down with it.
"Oil, then yen, and then some flaky data, I'd say is what's going on here," Royal Bank of Scotland market strategist David Simmonds said.
"These currency markets they are not so much climbing a wall of worry, they are just frozen on this wall of worry right now, and that isn't going to change with oil prices as firm as they are."
Oil prices hit a high of $44.24 per barrel, marking the highest since crude futures were launched on the New York Mercantile Exchange in 1983.
Stock market gains in most of the region, apart from Tokyo, offered some support.
Singapore shares were at their highest since March 2001 in afternoon trade.
Still, north Asian currencies held up best on Tuesday - the Taiwan dollar eked out a small gain while the Korean won ended just weaker - while the south-east Asians all ended in negative territory.
The dollar was supported by a rise in the Institute for Supply Management's manufacturing index - which was also positive for Asia as a major exporter to the United States - after a heightened security alert saw it lose ground on Monday.
In Singapore, the Purchasing Manager's Index fell 3.3 points in July from June, the first fall since February and the biggest since May 2000.
The Singapore dollar weakened to 1.72 per dollar before steadying.
Last week, the Singapore dollar fell to near 1.73, a two-month low, before recovering with what traders said was some assistance from the Monetary Authority of Singapore.
"We would hesitate to go long at current levels, but would use rallies toward the upper end of the Singapore dollar's recent range to go short dollar/Sing medium-term," BNP Paribas senior currency strategist Thio Chin Loo said in a report.
Asia imports most of its oil, and the high prices have raised worries about inflation pressure and slowing growth in the region.
Those concerns were not helped by comments from Opec President Purnomo Yusgiantoro on Tuesday.
"The oil price is very high, it's crazy. There is no additional supply," Purnomo told reporters.
Adding to Asia's worries, the start of a rate rise cycle in the United States and uncertainty over efforts to slow China's economy have made it a less attractive investment destination.
Proprietary data from UBS showed that in the week to July 30, Asia-Pacific equity markets saw a net outflow of $388 million.
The four-week moving average showed an outflow of $472 million.