TAIPEI (REUTERS) - Taiwan's air force scrambled for a second straight day on Saturday (Feb 20) after a dozen Chinese fighter aircraft and bombers carried out drills close to Taiwan-controlled islands in the disputed South China Sea, the defence ministry in Taipei said.

Beijing - which sees Taiwan as a breakaway province to be reunified, by force if necessary - has carried out repeated air missions in the southwestern corner of Taiwan's air defence identification zone in recent months, mostly near the Pratas Islands.

After nine Chinese air force aircraft flew near the Pratas Islands on Friday, the Taiwanese Defence Ministry said it tracked 11 aircraft on Saturday - eight fighter jets, two nuclear-capable H-6 bombers and an anti-submarine aircraft, also near the islands.

It said Chinese naval forces were also involved but gave no details.

Taiwan's air force warned the Chinese aircraft to leave and deployed missile systems to monitor the activity, the ministry said.

China has not commented on the last two days of activities.

It previously said such manoeuvres were a response to "collusion" between Taipei and Washington, Taiwan's main international backer and weapons supplier, and to safeguard Chinese sovereignty.

A spokesman for the US State Department on Saturday repeated a call for Beijing "to cease its military, diplomatic, and economic pressure against Taiwan," adding that it should "instead engage in meaningful dialogue with Taiwan's democratically elected representatives."

The Pratas Islands sit in the top part of the South China Sea and are also claimed by China.

Lying roughly between southern Taiwan and Hong Kong, they are only lightly defended by Taiwan and are considered by some security experts as vulnerable to Chinese attack due to their distance - more than 400km - from mainland Taiwan.

Chinese aircraft fly in the southwestern corner of Taiwan's air defence zone on an almost daily basis, though the last such large-scale activity was on Jan 24 when 12 Chinese fighters were involved.

Taiwan on Friday unveiled a reshuffle of senior security officials including the appointment of a new, US-trained defence minister, to help bolster military modernisation and intelligence efforts in the face of what it sees as a rising Chinese threat.