Congress vice president Rahul Gandhi and Union minister of state for power R K Singh visited the accident site.
Taking a break from his Gujarat election tour, the Congress vice president visited the district hospital and NTPC premises and enquired about the incident from officers present.
He was accompanied by senior party leader Ghulam Nabi Azad and Congress state president Raj Babbar.
"How many workers were working there?" he was heard asking officers at the Unchahar unit of NTPC.
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Azad demanded a high-level probe by an outside agency to bring out the fact.
Rahul also came face to face with Singh during his NTPC visit.
When asked about the incident, Singh said there could be two issues -- design or maintenance. "We are looking into both the aspects," he said.
On charges that the plant unit was commissioned ahead of time, he said it was not done in haste.
"The work was completed before March and after two-three months of trial, it was commissioned," he said.
Deputy CM Dinesh Sharma and UP power minister Srikant Sharma also visited Raebareli and met the injured.
Gandhi took a break from his ongoing 'Navsarjan Yatra' in poll-bound Gujarat and rushed to Rae Bareli, his mother Sonia Gandhi's Lok Sabha constituency, to meet the families of victims of the explosion.
The Congress president has expressed shock at the "terrible tragedy".
Azad said she has been discharged from hospital day before yesterday. Had she been well, she would have visited the families of the victims, he said.
UP Principal Secretary (Home) Arvind Kumar told reporters in Lucknow that the toll in the NTPC boiler blast has risen to 26.
The NTPC has initiated a probe to ascertain the reasons behind the blast.
In a statement, the National Thermal Power Corporation (NTPC) has said that at unit number six of its Unchahar plant, there was a sudden abnormal sound at 20-meter elevation around 3:30 yesterday afternoon.
It added that around 80 people were rushed to the NTPC Hospital, most of whom were discharged after first-aid.
The 1,550-MW plant supplies electricity to nine states, according to officials, and employs around 870 people.
Prime Minister Narendra Modi had said that he was "deeply pained" by the accident at the power plant.
Modi approved ex-gratia payment of Rs 2 lakh each for the families of those killed.
"Prime Minister @narendramodi has approved an ex-gratia of Rs 2 lakh each for the next of kin of those who have lost their lives due to the accident at the NTPC plant in Raebareli, Uttar Pradesh. PM has approved Rs. 50,000 each for those injured due to the accident," PMO India said on Twitter.
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