The US moved large numbers of special-operations aircraft, troops, and equipment into the Caribbean area this week, The Wall Street Journal reported on Tuesday.

According to US officials and open source flight-tracking data, at least ten V-22 Osprey tiltrotor aircraft and C-17 cargo aircraft arrived in the region on Monday. According to one of the sources, the aircraft were transporting military personnel and equipment. It is unclear what type of troops and equipment the aircraft were carrying.

The spokesperson for the US Southern Command, which is responsible for US military operations in Latin America, declined to answer questions about the troop movements. He noted that regular rotation of equipment and personnel at any military facility is standard practice.

The White House and the Pentagon did not respond to requests for comment.

The US has been building up troops in the Caribbean since the beginning of the fall amid rising tensions with Venezuela.

For several months, the US has been carrying out strikes on ships it says are involved in drug trafficking and have ties to Venezuela. Also, it has seized oil tankers that are cooperating with Venezuela. President Donald Trump has repeatedly suggested that the US could strike Venezuelan territory.

AP reported on Tuesday that Russia has been evacuating the families of Russian diplomats from Venezuela since December 19. The Russian foreign ministry, however, denies this.