New Delhi, Sep 15 - With India going slow on the tri-nation gas pipeline, Iranian ambassador to India Seyed Mehdi Nabizadeh Tuesday said China is interested in the proposed multi-billion project but left the door open for New Delhi to rejoin the peace pipeline.

The Iranian envoy, however, remained quiet on whether Iran is holding talks with China over the tri-nation pipeline involving Iran, India and Pakistan.

The envoy invited India to rejoin the pipeline project but made it clear that the offer was not for the 'unlimited period'.

'Work on the project is progressing very fast and one should understand the urgency to join the pipeline,' the envoy told reporters here when asked whether Iran is setting any time frame for India to rejoin the project.

India has not officially quit the project, but has serious reservations about its viability due to differences over the pricing of the Iranian gas and security of the pipeline that will pass though violence-prone areas of Pakistan.