More than half of the 600-km-long Uttar Pradesh-Nepal border was sealed on Monday to prevent any kind of infiltration by 'undesirable elements' during the fourth phase of the Uttar Pradesh state assembly polls in 57 constituencies, spread across 10 districts, mostly lying along this border.

"The measure was necessitated in view of reports apprehending unauthorised entry of fake voters from across the border," a senior poll official told rediff.com in Lucknow.

"Not only have all the roads been sealed, but extensive patrolling was being carried out along the highly porous border," he said.

The seven-phase UP polls that commenced on April 7 will conclude on May 8.

In any case, these 57 constituencies were under the special scanner of the Election Commission on account of the presence of a large number of contestants with criminal antecedents.

As many as 118 of the 922 candidates in the fray were facing criminal charges, that included attempt to murder, culpable homicide, extortion, criminal intimidation, kidnapping and wrongful confinement.

Over 100 micro-observers are in the entire area to keep a close watch on each of the constituencies, while a deputy election commissioner from New Delhi was on the move on a helicopter to oversee the polling.

Of Bharatiya Janata Party's 52 candidates, 16 are facing criminal cases, followed by Bahujan Samaj Party's 12 and Rashtriya Lok Dal's 6, besides those from smaller political outfits and independents.

It is no wonder therefore that the EC had detailed nearly 66,000 personnel in addition to about 40,000 state policemen to handle the intensified security arrangements.

They are spread across 15,233 polling stations in the sprawling stretch of what is better known as UP's 'Terai' belt.