China says military flight off Malaysia was 'routine training'
The Malaysian foreign minister criticised the flight as an "intrusion" and said the government would lodge a protest with Beijing and summon the Chinese ambassador.
But a spokesman for the Chinese embassy in Kuala Lumpur said the "activities are routine flight training of the Chinese air force and do not target any country".
"According to relevant international law, Chinese military aircraft enjoy the freedom of overflight in the relevant airspace," he said.
The planes had not entered any other country's territorial airspace, the spokesman added in a statement.
The aircraft came within 60 nautical miles (110 kilometres) of the Malaysian part of Borneo, and did not respond to attempts to contact them, prompting Malaysia to scramble jets, according to the country's air force.
They turned back before entering Malaysian airspace over its territorial waters.
But Foreign Minister Hishammuddin Hussein said they had entered the country's "maritime zone" -- an area that extends much further from the coast -- and described the incident as a "breach of the Malaysian airspace and sovereignty".
Malaysia-China relations are usually warm but Monday's incident comes after a build-up in tensions over the sea, which is home to key shipping lanes and is believed to harbour rich oil and gas deposits.
Last year, a Chinese survey ship had a long stand-off with a Malaysian oil exploration vessel off Borneo.
Other claimants in the sea include Vietnam, the Philippines, Brunei and Taiwan.
The United States has also sent warships through the waters to assert international rights to freedom of navigation, angering China.