China scrambled fighter jets to investigate US and Japanese aircraft flying through its new air defence zone over the East China Sea on Friday as the regional clamour over the disputed airspace escalated.

The ministry of defence announced the move, which is the first time China is known to have sent military aircraft into the zone alongside foreign flights, stepping up its response to the challenge after its unilateral establishment of the zone. It previously said it had monitored US, Japanese and South Korean aircraft and had flown routine patrols in the area on Thursday.

The ministry's statement said two US reconnaissance aircraft and 10 Japanese early warning, reconnaissance and fighter planes had entered the zone.

The airforce "monitored throughout the entire flights, made timely identification and ascertained the types", defence ministry spokesman Shen Jinke told the official China News Service.

The Pentagon has yet to respond to the statement. Japanese officials declined to confirm details of any flights, saying that routine missions were continuing.

Late on Friday the US state department advised American commercial airlines to notify Chinese authorities of flight plans over the East China Sea. But a US administration official said that did not mean Washington accepted Beijing's jurisdiction, the Reuters news agency reported.

"The US government generally expects that US carriers operating internationally will operate consistent with Notams [Notices to Airmen] issued by foreign countries," the state department said in a statement.

"Our expectation of operations by US carriers consistent with Notams does not indicate US government acceptance of China's requirements."

The developments came as South Korea's Yonhap news agency said officials were discussing how to expand its own air zone.

In Taiwan, legislators issued an unusual joint statement chiding Ma Ying-jeou's government for its tempered response to China's announcement of the zone and urging it to lodge a tough protest with Beijing. The government later said it would convey its "stern position".

Earlier the European Union's foreign affairs chief Catherine Ashton expressed its concern that the zone had contributed to tensions in the region, saying that the EU called on all sides to exercise caution and restraint.

Foreign ministry spokesman Qin Gang urged the EU to handle the situation "objectively and rationally", adding: "European countries can have air defence identification zones. Why can't China?"

While such zones are common, China's is controversial because it includes the skies over islands known as the Senkaku in Japan and Diaoyu in China, which are the subject of a long-running territorial dispute, and overlaps zones established by Japan and South Korea. There has also been concern over China's warning that it would take unspecified "emergency defensive measures" if aircraft did not comply.

Taylor Fravel, an expert on regional security at the Massachusetts Institute of Technology, said establishment of the zone increased the potential for an incident in the air that could spark a larger crisis. But he said tensions might ease if China continued to clarify the nature of the zone and how it intended to deal with unidentified aircraft, especially those flying through the zone but not heading toward China.

"China has always chafed at Japan's adiz [air defence identification zone], which at some points is less than 150km from China … China probably wants to level the playing field with Japan and increase the pressure on Tokyo regarding the disputed islands," he said.

Japan does not acknowledge that ownership of the islands is disputed. The US does not have a position on their sovereignty but recognises Japan's administrative control and has said they are covered by the joint security pact.

Many analysts think China is laying down a long-term marker, but did not anticipate the forceful response it has received from the US as well as Japan.

"The Chinese government is not going to concede the substance," said June Teufel Dreyer of the University of Miami. "When circumstances are more conducive, they will try to enforce it more strictly in the future. This is a pattern we have noticed for decades."

Stephanie Kleine-Ahlbrandt, Asia-Pacific director at the US Institute of Peace, said the creation of its zone had its own momentum. "The danger in the announcement is that it empowers the People's Liberation Army, maritime agencies and netizens [internet users] to hold the government to account," she said. "Now people are transgressing the zone, they have to make it look to the domestic audience like they are serious. They have given birth to internal pressures."

Behind the immediate issues lie regional concerns about China's growing strength, Beijing's unease at Japanese prime minister Shinzo Abe's determination to strengthen his country's forces, and questions about the US presence in and commitment to the region. US vice-president Joe Biden will visit Beijing, Tokyo and Seoul on a trip beginning this Sunday which is likely to be dominated by discussions of the zone.

"I think the only problem is Japan because it has taken a confrontational policy. They want clashes and to drag America into military containment against China," said Yan Xuetong, a foreign relations scholar at Tsinghua University.

"The international community has ignored the roots of this … Abe has clearly stated that his fundamental goal is to revise the constitution [under which Japan renounces war] and he needs security tensions to legitimise his efforts."

Tokyo's military ambitions are particularly sensitive because many in China say Japan has not adequately recognised or atoned for its brutal occupation.