Esper has visited several regional US allies including Japan and Australia in his maiden tour abroad following his confirmation as Pentagon chief last month.

His diplomatic offensive comes as Washington seeks to reassure its traditional friends of its support in the face of China's more assertive foreign policy and military posture.

Including Mongolia in his trip is partly a reflection of the landlocked country's geo-strategic importance -- sandwiched between China and Russia.

"It is my deep privilege to be here, to be with you and to have the opportunity to look at different ways we can further strengthen the ties between our two countries," he said.

Esper was invited to name a horse in a traditional gesture of respect for visiting state guests.

He chose the name Marshall, after the general and diplomat who drafted the US-funded plan for the reconstruction of Europe after World War II.

Mongolia depends on Russia for three-quarters of its oil and China for most of its trade, but sees US relations as a hedge against its neighbours.

Earlier on his Asia tour, Esper had underlined the need to compete with the Chinese as they sought to "expand their interests and their tentacles around the globe."

He also warned of China's efforts to "coerce its neighbours into activities designed for Beijing's benefit."

burs-gle/mtp