HANOI (Reuters) - Recent activity by China’s strategic bombers in the South China Sea’s Paracel Islands seriously violated Vietnam’s sovereignty over the disputed territory, Vietnam’s foreign ministry said on Monday.

FILE PHOTO: A Vietnamese naval soldier stands quard at Thuyen Chai island in the Spratly archipelago, January 2013. REUTERS/Quang Le

China’s air force said bombers such as the H-6K had landed and taken off from islands and reefs in the South China Sea as part of training exercises last week.

The flights “increase tensions, cause regional instabilities and are not good for maintaining a peaceful, stable and cooperative environment in the East Sea,” foreign ministry spokeswoman Le Thi Thu Hang said in a statement, using the Vietnamese name for the South China Sea.

The Philippines also expressed “serious concerns” on Monday over the presence of the bombers in the area and its foreign ministry has taken “appropriate diplomatic action”.

Vietnam and China have long been embroiled in maritime disputes in the South China Sea. The Philippines, Malaysia, Brunei and Taiwan also have claims to parts of the potentially energy-rich maritime territory.

“Vietnam demands that China stop these activities, cease militarization of the area, and strictly respect Vietnam’s sovereignty over the Hoang Sa islands,” Hang said, referring to the Paracels.

Hang said the presence of the bombers in the area has an adverse impact on ongoing negotiations between China and the Association of Southeast Asian Nations on a Code of Conduct in the South China Sea.

In Beijing, Chinese Foreign Ministry spokesman Lu Kan urged other countries not to over-interpret what he called a routine military patrol.

“We hope that relevant parties do not read too much into this,” Lu Kang told a daily news briefing.

Earlier this month, Vietnam also asked China to withdraw military equipment from the nearby Spratly Islands in the disputed waters, following media reports that China had installed missiles there.

In response, China said its deployment of defense equipment and troops on the islands was its right, adding that the equipment helped protect the peace and stability of the region and “does not target any country”.

Vietnam’s state oil firm PetroVietnam has said maritime tensions with China will hurt its offshore exploration and production activities.

In March, the company told Spanish energy firm Repsol to halt an oil project offshore of Vietnam under pressure from China.

Last week, a unit of Russian state oil firm Rosneft also expressed its concern that its recent drilling in the area could upset China.