CARACAS, Dec. 23 (Xinhua) -- Venezuela's government on Sunday demanded respect for its sovereignty and international law, saying oil exploration ships working for neighboring Guyana violated its maritime borders.

In a statement, the Foreign Affairs Ministry said the incident occurred on Saturday, when naval patrols "detected the unusual presence in Venezuela's territorial waters of two seismic exploration vessels."

The vessels, identified as "RAMFOR under the Bahamas flag and DELTA MONARCH under the flag of Trinidad and Tobago, were contracted by the transnational ExxonMobil," the ministry said.

The vessels were in Venezuela's Orinoco Delta, officials said.

In an exchange with Venezuela's navy, the captains of the vessels said they had the operation permission of Guyana's government in the area, according to the ministry.

Venezuela and Guyana have had a long-running border dispute over the oil-rich region of Esequiba, which flared up again in 2015 after ExxonMobil announced the discovery of an oil deposit in the area.

Despite the "unacceptable violation of national sovereignty," Venezuela reiterated its willingness to dialogue with Guyana -- in keeping with a 1966 treaty calling for a peacefully negotiated solution -- and its determination to defend its territorial jurisdiction.

Guyana denies the vessels were in any violation, and accused Venezuela of illegally intercepting the ships.