Dhaka, Bangladesh (BBN)-When Narendra Modi takes the oath that officially makes him India's 15th prime minister on Monday evening, neighboring South Asian nations will all have representatives to witness the event.

The only leader who will be missing is Bangladesh's Prime Minister Sheikh Hasina, who is on an official visit to Japan and is being represented by parliament speaker Shirin Sharmin Chaudhury, reports turkishpress.com.

Hasina and her rival Khaleda Zia, the leader of the opposition Bangladesh National Party, were both quick to congratulate Modi's Bharatiya Janata Party's landslide election victory but Modi's comments, made during the election campaign, about deporting "illegal" Bangladeshi migrants has also sparked tension in Bangladesh's political area.

The announcement of a separate unit in the home ministry to tackle immigration from Bangladesh has intensified that unease.

“It was not only Modi’s point to win the election, but he would also keep the issue alive and work on it, as it is his party’s political view," says Tasneem Siddiqui, a Dhaka University academic who focus on refugees and migrations.

"Bangladesh government and media should articulate the issue regularly right from the beginning of the new Indian government led by Modi.”

Golam Mortoza, editor of Weekly Shaptahik and a political analyst, said Modi may use the issue of migrants in negotiations with Bangladesh and public speeches.

 “Modi government can initiate a process of identifying the Muslim Bangladeshis in India," he said.

"Some push-back also may take place. Bangladesh government would face an awkward situation as a result of this and they would neither be able to bargain on the issue nor accept the situation."

Media reports suggest that when Hasina congratulated Modi, most of the conversation was focused on a water-sharing agreement for the river Teesta, which runs through both countries.

The agreement was supposed to be signed by Modi's predecessor Manmohan Singh, but faced strong objection from Mamata Banerjee, chief minister of eastern Indian state West Bengal.

According to Mortoza, there is a chance the Teesta agreement will be put on ice because Banerjee, whose consent is vital, will not change her mind and Modi may not agree with the old terms. Professor Nazmul Ahsan Kalimullah, chairman of the National Election Observation Council, said however that he would not be surprised if Modi sees the Teesta water-sharing agreement as a political opportunity.

Kalimullah said the Teesta agreement, which would end a long-running dispute over how to share the river's resources, could even see Modi make Bangladesh the first destination for a foreign trip in a bid to further develop bilateral relations.

BBN/ANS/AD-26May14-7:40pm (BST)