Ending a two-day visit to Istanbul, Kerry told reporters Sunday that he believed that “it would be more helpful [for Erdogan] to wait for the right circumstance…. We’re trying to get off the ground, and we would like to see the parties with as little outside distraction as possible.”

He said this was one of a number of “important reasons” why Erdogan shouldn’t go on the trip, and implied that the Turkish leader hadn’t made a final decision on the plan.

Kerry met with Foreign Minister Ahmet Davutoglu and other Turkish officials, but didn’t see Erdogan.

Both the Israelis and Palestinian Authority PresidentMahmoud Abbas have voiced unhappiness with Erdogan’s plans.

Erdogan has been pushing for Israel to ease its partial embargo on the entry of goods into Gaza, and has announced plans to visit the impoverished seaside zone in the next few weeks.

The move could complicate efforts to begin a rapprochement between Turkey and Israel. Former allies, they have been estranged since Israeli soldiers killed Turks when a Turkish flotilla sought to breach the naval blockade of Gaza in 2010.

At President Obama’s urging, Israeli Prime MinisterBenjamin Netanyahu formally apologized to Turkey last month. An Israeli delegation is scheduled to meet with Turkish officials Monday to discuss compensation for the families of the Turks who were killed.

On another subject, Kerry acknowledged some frustration with the slow delivery of U.S. aid to Syrian rebels, but said U.S. officials have made progress in speeding deliveries, and insisted future aid will arrive more quickly. Aid that Kerry announced in February hasn’t yet been delivered to rebel forces, and it’s unclear how long it will take for delivery of a new round of nonlethal aid that Kerry announced at an international meeting in Istanbul on Saturday.

Kerry promised he would “press as hard as I can to make sure it’s a matter of weeks — it has to happen quickly.”

Rebel fighters have complained that the United States hasn’t given them enough military help, and the aid it has approved has been slow in coming. In late February, Kerry announced that the United States would provide $60 million in food and medicine, in a package that for the first time would be sent directly to rebel fighting units. That amount will now be more than doubled, to $123 million.

Kerry said it is still unclear what kind of gear will be bought with the new money. He said the Syrian opposition’s Supreme Military Council would be given its choice of goods, which may include body armor, night-vision goggles and armored vehicles.

U.S. officials say they remain opposed to providing arms, partly because they fear weaponry could end up in the hands of the religious extremists who are a growing part of rebel forces. But other U.S. allies, including Qatar and Saudi Arabia, are funneling arms to the opposition fighters.