The "militarization" of the East Vietnam Sea is threatening peace in the waterway, the EU's top diplomat said Monday in Hanoi, echoing warnings from the U.S. as pressure mounts against Beijing's ambitions in the region.

China has been accused of deploying warships, arming outposts and ramming fishing vessels in the resource-rich sea, sparking ire from other claimants.

On Monday, the European Union's foreign policy chief Federica Mogherini said the bloc was concerned over "increasing tension" in the area.

"We believe that this tension, this militarization, is definitely not conducive to a peaceful environment," she added.

Beijing says it has sovereignty over the majority of the sea based on the so-called nine-dash line it uses to back its claims.

The long-running spat was center stage at a meeting of Southeast Asian foreign ministers last week, where U.S. Secretary of State Mike Pompeo urged countries to push back against Chinese "coercion" in the sea.

Hanoi has emerged as one of Beijing's most vocal critics in the waterway, a key global shipping route believed to hold vast oil and gas reserves.

Tensions between Vietnam and China have soared after a Chinese geological survey vessel entered waters around the Vietnamese Spratly islands in early July.

Vietnam has repeatedly called for the ship to leave in statements issued by the foreign ministry, while experts keep saying China is breaking international law.

The U.S., EU and Australia have all called for freedom of navigation in the East Vietnam Sea.