RIYADH, Saudi Arabia — President Obama reassured King Abdullah of Saudi Arabia on Friday that the United States remained committed to strengthening the moderate opposition in the Syrian civil war, administration officials said.

But aides declined to reveal whether Mr. Obama and the king agreed to any significant expansion of the covert program to train and arm the Syrian opposition. Relations between the two countries have become strained in recent months, in part over Saudi frustration with the United States’ reluctance to provide arms that could end up in the hands of jihadists and extremists in Syria.

“The emergence of some more extremist elements within the opposition only reinforces the need to strengthen the more moderate opposition,” a senior administration official told reporters in Riyadh after a two-hour meeting at the king’s palatial desert compound. “We have been improving that coordination and planning with our partners and allies.”

Mr. Obama met with Abdullah at the end of the president’s weeklong tour through Europe, which focused primarily on bolstering the European response to Russia’s military intervention in Ukraine. In Saudi Arabia, the president shifted his focus to another region racked by conflict.