The neighbouring countries are involved in a long-running dispute about which country controls the 160,000-square-km Esequibo area, which is the subject of an ongoing case at the International Court of Justice (ICJ).
The northwest portion of the block, close to Venezuela, has remained in force majeure as the Exxon group has been unable to complete exploration there.
"This incursion is a matter of grave concern," Ali said.
"Guyana's maritime boundaries are recognised under international law. This is a serious development concerning our nation's maritime territory. We will not tolerate threats to territorial integrity."
"During this incursion, the Venezuelan vessel approached various assets in our exclusive waters, including FPSO Prosperity," Ali said in a statement.
The Venezuela communications ministry did not immediately respond to a request for comment.
Guyana summoned the Venezuelan ambassador to meet with its foreign minister and discuss Guyana's strong objections, and its embassy in Caracas has been advised to lodge a formal complaint with Venezuela, Ali added.
Guyana will also formally report this incident to the ICJ and engage with international partners like CARICOM, the statement added.
The Guyanese government has also deployed unspecified air assets, Ali added.
The Organisation of American States (OAS) condemned the Venezuelan incursion in "Guyana's internationally recognised maritime territory".
The incident was a violation of Guyana's territory, the United States Bureau of Western Hemisphere Affairs said on X.Â
"Further provocation will result in consequences for the Maduro regime," it added.
with AP
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