RIYADH, Saudi Arabia — Secretary of State John Kerry said Monday that the Syrian opposition is capable of properly handling the military support it receives.

“There is no guarantee that one weapon or another might not at some point in time fall into the wrong hands,” Mr. Kerry said in a joint news conference in Riyadh with the Saudi foreign minister, Prince Saud al-Faisal. “But I will tell you this: There is a very clear ability now in the Syrian opposition to make certain that what goes to the moderate, legitimate opposition is, in fact, getting to them, and the indication is that they are increasing their pressure as a result of that.”

Mr. Kerry’s comments followed a conference in Rome last week on the issue of building support for a coalition of opponents to the Syrian government of President Bashar al-Assad, which Mr. Kerry attended. He spoke to concerns that aid that was meant for the Western-backed group might be diverted into the hands of extremists.

While President Obama has decided that the United States will not provide arms to the rebels, Mr. Kerry announced last week that it would send food and medical supplies to the armed wing of the Syrian opposition. The United States has also been training a select cadre of Syrian rebels in Jordan under a covert program run by the C.I.A., officials have said.