Worries about a debt default in Ukraine and growing tensions between the West and Russia over Ukraine's future following the ousting of President Viktor Yanukovych at the weekend have fueled risk aversion in global markets.
(Read more: Risk of a bank run heightens in Ukraine)
The yield on 10-year Treasurys hit a three-week low of 2.66 percent overnight, while the U.S. dollar index rose to its highest level in about two weeks as jittery investors sought out safe-havens.
Russia on Wednesday ordered a drill to test the combat readiness of its armed forces, fueling investor jitters over Ukraine and helping send the Russian rouble to a five-year low at about 36.06 per dollar.
In addition, the Turkish lira fell 0.8 percent overnight to a three-week low of 2.2530 per dollar as pressure mounted on Prime Minister Tayyip Erdogan to step down amid a corruption scandal that has embroiled the government.
"We are seeing risk aversion in general resurface," said Nizam Idris, managing director, head of strategy, fixed income and currencies at Macquarie Bank. "The tension in Ukraine is one reason for this – Ukraine's debt is largely funded by Russia, so if Ukraine defaults then Russia bears the brunt."
Brazil's central bank meanwhile hiked its key interest rate by 25 basis points to 10.75 percent on Wednesday, breaking a streak of six straight 50-basis-point hikes. Still, the move highlighted that emerging markets continue to see a need take action to prop up weak economies, analysts said.
(Read more: Brazil slows interest rate hikes to shield weak economy)