BEIJING (Reuters) – Apple chief executive Tim Cook nudged China on Saturday to open up and said the future would depend on global collaboration, as the United States and China remained locked in a bitter trade dispute.

“We encourage China to continue to open up, we see that as essential, not only for China to reach its full potential, but for the global economy to thrive,” Cook said at a China Development Forum in Beijing.

Despite official pledges and repeated assurances that China would continue to open its markets, some analysts worry that its reform project has slowed or even stalled under President Xi Jinping, who has sought greater control over the economy and a bigger role for state-owned firms at the expense of the private sector.

Cook’s comments come as Apple weathers sinking sales in China because of a contracting smartphone market, increasing pressure from Chinese rivals, and slowing upgrade cycles. The company reported a revenue drop of 26 percent in the greater China region during the quarter ending in December.

Before those results came out, in a January letter to investors, Cook blamed the company’s poor China performance on trade tension between the United States and China, suggesting that pressure on the economy was hurting sales in China.