By Arathy Somasekhar

HOUSTON (Reuters) -Oil prices rose slightly on Monday after the United States vowed to keep attacking Yemen's Houthis until the Iran-aligned group ends its assaults on shipping, while Chinese economic data buoyed hopes for higher demand.

U.S. President Donald Trump said on Monday he would hold Iran responsible for any attacks carried out by the Houthi group that it backs in Yemen, as his administration expanded the biggest U.S. military operation in the Middle East since Trump returned to the White House.

Brent futures rose 49 cents, or 0.7%, to $71.07 a barrel, while U.S. West Texas Intermediate crude futures gained 40 cents, or 0.6%, to $67.58.

The Red Sea port city of Hodeidah and the Al Jawf governorate north of the capital Sanaa were targeted on Monday, the Houthis' Al Masirah TV said.

Chinese economic data also supported prices. Retail sales growth quickened over January-February in a welcome sign for policymakers seeking to boost domestic consumption, though unemployment rose and factory output eased.

China's crude oil throughput in January and February rose 2.1% versus a year earlier, official data showed on Monday, supported by a new refinery and holiday travel, but weak refining margins persisted.

"The combination of increased stimulus from China and the heightened attack by the Houthi rebels is providing a significant boost (to oil) this morning," said Phil Flynn, senior analyst with Price Futures Group.

The U.S. dollar eased against a basket of currencies as investors worried about the economic fallout from Trump's protectionist trade policies. A weaker dollar makes oil less expensive for overseas buyers, boosting demand.

Oil rose slightly last week, though Brent is still down almost 5% this year on concern over a global economic slowdown driven by escalating trade tensions between the U.S. and other nations.

OPEC+ oil producers' plan to raise oil output from April has also pressured prices. However, the prospect of tighter U.S. sanctions against Iran more than offsets the gradual OPEC+ production increase, said Saxo Bank head of commodity strategy Ole Hansen.

"China's plans to boost consumption and fresh Red Sea risks" are supporting the market on Monday, he added.

Trump said he would speak to Russian President Vladimir Putin on Tuesday about ending the Ukraine war, with territorial concessions by Kyiv and control of the Zaporizhzhia nuclear power plant likely to feature prominently in the talks.

"The negative to crude is focused on the tariffs and a Russia/Ukraine peace negotiation which would likely increase Russian crude to the world market," said Dennis Kissler, senior vice president of trading at BOK Financial.

U.S. crude oil stockpiles are expected to have risen last week, while distillate and gasoline inventories likely fell, a preliminary Reuters poll showed on Monday. Industry data is expected on Tuesday, while official government data is expected on Wednesday.

(Reporting by Arathy Somasekhar in Houston and Alex Lawler in London. Additional reporting by Sudarshan Varadhan in SingaporeEditing by David Evans, David Goodman, Sharon Singleton and Rod Nickel)