NEW DELHI (Reuters) - India's foreign minister said on Wednesday she was in hospital being treated for kidney failure and undergoing tests for a possible transplant, an announcement that raises questions over how long she can stay in the job.

Sushma Swaraj, a senior leader of Prime Minister Narendra Modi's nationalist government, said she was on dialysis at the All India Institute of Medical Science, a top government hospital.

"I am undergoing tests for a kidney transplant. Lord Krishna will bless," Swaraj said from her authorized account on social network Twitter.

The 64-year-old politician has been sidelined by poor health on a number of occasions since Modi's Bharatiya Janata Party swept to power in 2014. There has been no announcement that she will formally delegate her duties while she is unwell.

Her team was recently reinforced by veteran journalist M.J. Akbar, who has traveled extensively since being named minister of state. That has left the other minister of state, former army chief of staff V.K. Singh, to take the lead on ensuring the security of Indian citizens abroad.

Although Swaraj is one of Modi's most experienced ministers, the premier has made foreign policy very much his own domain, traveling the world and working to strengthen ties, especially with the United States.

(Reporting by Douglas Busvine; Editing by Malini Menon and Clarence Fernandez)