Brazil says that it is deploying troops along its border with Venezuela after the Venezuelan government announced plans to incorporate an area controlled by Guyana into its territory.
The oil-rich Essequibo region has been in dispute since the 19th Century when Guyana was a British colony.
Venezuela renewed its land claims after offshore oil and gas reserves were discovered a few years ago.
Tensions have been rising since a referendum on Sunday in Venezuela.
More than 95% of voters are said to have supported the government’s claim to Essequibo.
Venezuela’s leader Nicolás Maduro has since asked the state oil company to issue extraction licenses there and proposed that the National Assembly pass a bill to make the area part of Venezuela.
The measures are cause for concern across the region. While Guyana has its troops on high alert, the Brazilian army has said that it is moving more soldiers to the border city of Boa Vista, the capital of Roraima state, as well as bringing in more armed vehicles.
However any military incursion by Venezuela will be logistically challenging, Venezuelan soldiers would need to pass through Brazilian territory if they enter Essequibo because of challenging terrain elsewhere.
According to AFP news agency, Brazil’s army has said it is reinforcing its presence in the region as part of efforts to “guarantee the inviolability of the territory”.
A Guyanese army helicopter with seven people on board was reported missing near the Venezuelan border on Wednesday. However, the Guyanese Chief of Staff, Omar Khan, said there was “no information suggesting Venezuela was involved”.
Source : BBC