BRASILIA (Reuters) - The Brazilian army stepped up patrols on the border with Venezuela on Friday, a day after picking up five deserting Venezuelan soldiers amid rising tensions between the two countries.

Brazil’s defense ministry said in a statement that the unarmed soldiers were found on Thursday on an indigenous reservation on the Brazilian side of the border.

“They presented themselves as deserters and are being debriefed to see if they were involved in a recent attack on a base in Venezuela,” a Brazilian military source with knowledge of the situation told Reuters.

The source said their motive for deserting had not been established yet but he suspected they had been involved in a Dec. 22 raid on an infantry garrison in southern Venezuela.

President Nicolas Maduro said on Monday that 11 people were arrested in connection with the raid on a remote military outpost in the southern state of Bolivar state on Sunday. He said some suspects fled across the border to Brazil with stolen weapons.

Venezuela accused Peru, Colombia and Brazil - adversaries of socialist Maduro which recognize opposition leader Juan Guaido as the rightful president - of complicity with the attack, in which one Venezuelan soldier was killed. All three countries’ governments have denied involvement.

Hundreds of members of Venezuela’s security forces have left their country in last few years, encouraged by Guaido to desert. Most have entered Colombia, but dozens have fled to Brazil where they have been received as refugees.

The Brazilian military, however, has tried to avoid conflict with its Venezuelan counterpart despite virulent criticism of Maduro’s government by Brazil’s far-right President Jair Bolsonaro.