Saudi
Arabia and its Gulf Arab allies began air strikes in Yemen
against Houthi fighters besieging the southern
city of Aden.
Tensions in the Middle East appear positive for oil and safe-haven yen.
The potential threat to oil supplies from the Gulf boosted U.S. crude $1.81 to $51.02, while Brent crude rose $1.56 to $58.04 a barrel.
The dollar broke down to a one-month trough on the yen around 118.94 JPY=, while yields on 10-year U.S. Treasuries ticked down to 1.91 percent.
The greenback continued to drift after last week's fluctuations. Measured against a basket of currencies, the dollar eased 0.3 percent to 96.695, just above a three-week trough of 96.387 set on Tuesday. Earlier in March, it scaled a 12-year peak of 100.390.
The euro EUR= was last at $1.0989, well off a 12-year trough of $1.0457 plumbed two weeks ago, says Reuters.
Saudi Arabia and its allies from the Gulf region launched military operations including air strikes in Yemen on Thursday, to counter Iran-allied forces besieging the southern city of Aden where the U.S.-backed Yemeni president had taken refuge.
As Yemen slid towards civil war, it became a crucial front in mostly Sunni Saudi Arabia's rivalry with Shi'ite Iran, which Riyadh accuses of stirring up sectarian strife throughout the region and in Yemen with its support for the Houthis.
