The PMO website, along with those of the Lok Sabha, Rajya Sabha and key ministries such as finance and defence, were not accessible for a few hours this evening.
While the Press Information Bureau's website remained down, the department said in a Twitter message: "Govt clarifies that there was no cyber attack or hacking of Govt websites. Due to malfunctioning of some equipment, some sites were down."
It said services would be restored soon, although no time line was given.
The officials said the websites encountered some technical glitches because of which they became inaccessible.
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"From evening there has been a glitch. It is being looked into by the National Informatics Centre and the websites which are encountering problems will be restored," a senior official said.
While efforts at reaching the websites of the law, oil and agriculture ministries yielded no results, a message, "the specified URL cannot be found", appeared on the website of the Finance Ministry.
Websites of the information and broadcasting ministry, Department of Telecommunications and the Department of Electronics and Information Technology also remained unavailable.