The appeal, signed by more than 200 Tibet campaign organisations, urged the "governments around the world to issue a public statement of concern about the crisis and to continue to raise with China in the strongest diplomatic terms."
They urged the world leaders to convey the message to China's leaders at every possible opportunity to withdraw paramilitary forces from Ngaba, unconditionally release all the detainees and to give unfettered access to international observers and media.
The international Tibet Network has also initiated "Global Week of Action for Ngaba", a concerted campaign to highlight the situation in northeastern Tibet.
The Chinese government imposed military blockade of the monastery in March this year following the protests by the local Tibetans over the self-immolation by Phuntsog, a monk of Kirti monastery, in protest against China's brutal suppression of peaceful protests which shook Tibet in 2008.
The crackdown has so far left two elderly Tibetans dead and over 300 monks detained.