On the days before and after US secretary of State Rex Tillerson embarked on his first official trip to Africa, one issue has risen as the main concern among American officials: China’s ascendant role in the African continent.

Testifying in front of the US armed services committee on Mar. 6, the top US general for Africa Thomas Waldhauser said they were “carefully monitoring Chinese encroachment and emergent military presence” in Djibouti. The Horn of Africa nation is home to the only permanent US military installation in Africa. But last year, China opened its first overseas naval base there too, provided loans to the country, and built a railway connecting its seas to the Ethiopian hinterland to improve regional trade.

But the recent US unease was linked to Djibouti terminating the contract of one the country’s biggest port operators, the Dubai-owned DP World. The company called the move an illegal seizure, prompting US officials to speculate if president Ismail Omar Guelleh could also kick them out at will in the future and if he could hand over the port to China. “If they did [give the port to China], down the way that restricts access, that restricts the [US] navy’s ability to get in there and offload supplies,” Waldhauser warned.

Afterward, Djibouti signed a deal to increase the number of cargo containers handled at the port with the Singapore-based Pacific International Lines that works with China Merchants Port Holdings, which already has a stake in the Djibouti port.

A few hours after Waldhauser’s comments, Tillerson gave a speech at the University of Virginia in which he lamented Beijing’s economic engagement model, saying it undermined democracy and mired African countries in debt. When he landed in Ethiopia a day later, he warned African nations from forfeiting their sovereignty and to “carefully consider” the terms of their agreements with China. “We are not in any way attempting to keep Chinese dollars from Africa,” he added.

Reuter/Ahmed Jadallah DP World is out.

Despite giving millions of dollars in aid, China has eclipsed the US in Africa in many ways: providing loans, financing much-needed infrastructure, competing for resources like oil and minerals, increasing its trade share, and spreading its ideological influence. And despite Africa’s immense economic growth, “there has not been much traction on the economic and diplomatic aspects of US-Africa relations,” says Brahima Coulibaly, the director of the Africa Growth Initiative at the Brookings Institution. This allowed partners like China to fill the void, hence strengthening its place in the continent.

As the continent looks to the East for aid and trade, US officials are increasingly focused on security and counterterrorism efforts. This is evident in all the nations Tillerson has or is due to visit—Ethiopia, Djibouti, Kenya, Chad, and Nigeria—which continue to fight terrorist groups like al-Shabaab or Boko Haram. The Trump administration has also given its military a wider scope to launch airstrikes in Somalia, is supporting African governments in intelligence and reconnaissance efforts, and is building a drone base in Niger, where eight US and Nigerien soldiers died in an ambush last year.

Coulibaly says unless Tillerson’s trip produces a clear dialogue that will inform US-Africa strategy, “the United States risks falling behind.”

Correction: A previous version of this story said the Singapore-based Pacific International Lines was awarded the contract to manage the port of Djibouti. They weren’t. The new contract was to increase the number of containers passing through the port, not the management of the port.