Malfunctioning Electronic Voting Machines (EVM) have again marred elections in India and raised question about the reliability of the devices.

Election Commission (EC) officials blamed heat waves for affecting the machines.

On Monday numerous media reports emerged about EVMs not working, with opposition parties claiming tampering as four Lok Sabha, or Lower House of the Indian Parliament, seats and nine assembly constituencies held by-elections.

However, the EC has called the large number of EVM failures exaggerated and said defective machines did not diminish the credibility of elections, the Press Trust of India (PTI) reported.

According to media reports, the EC was also ridiculed after its officials said the EVM machines malfunctioned due to heat waves in the northern region of Uttar Pradesh.

However, the EC assured leaders of the ruling Bharatiya Janata Party (BJP) and leaders of the opposition Samajwadi Party (SP), Congress and Rashtriya Lok Dal that the elections were going well.

The poll panel did release a statement saying the failure of the voting machines was not unusual, according to a PTI report. It said there were always “sufficient reserves” of EVM and Voter-Verified Paper Audit Trail (VVPAT) machines to replace defective ones at polling stations and kept secured with sector officers who took less than 30 minutes to replace the defective machines.

A paper trail machine shows the voter a slip confirming that his vote has gone to the same candidate he had chosen on the EVM. This cross-verifying procedure, introduced to foolproof the EVMs, was also under scrutiny as reports emerged about VVPAT malfunctions.

While opposition leaders demanded a new vote be held in places where EVMs were not replaced after more than one and a half hours of malfunctioning, the BJP delegation claimed 197 booths across the Lok Sabha seat of Kairana and state assembly constituency of Noorpur in Uttar Pradesh faced long periods of EVM failures.

The BJP has been wary in Uttar Pradesh as it recently lost two crucial constituencies – Phoolpur and Gorakhpur – to an anti-BJP coalition in byelections. Earlier on Monday, SP head Akhilesh Yadav alleged that hundreds of EVMs were malfunctioning in booths, especially where his party had a dominating support base.

He added that police also used batons on voters to dissuade them from voting. The BJP said those were irresponsible comments as the opposition was going to lose the Kairana election.

However, BJP officials later went to see the EC about the high-stakes Kairana and Noorpor polls.

The Palghar and Bhandara-Gondia constituencies in the western state of Maharashtra also had malfunctioning EVMs and VVPAT machines in several places. Technical glitches rendered machines dysfunctional, resulting in long queues of voters. The EC said the voting period was extended beyond 5pm.

The Congress, Nationalist Congress Party and Shiv Sena in Maharashtra have all alleged the malfunctions were created by the ruling BJP to give the party favorable election results.

In the past, many opposition parties raised allegations of EVM tampering, which the EC didn’t entertain. Last year, before the result of Gujarat elections came out, Congress went to the Supreme Court seeking directions to the EC to cross-check a minimum of 25% of EVM votes with the VVPAT paper trail.

However, the top court dismissed their plea.