Nobel laureate Muhammad Yunus and his newly named interim government set out Friday to restore "law and order" after a student-led uprising and deadly mass protests forced predecessor Sheikh Hasina into exile.

A day after returning home from Europe and vowing to "uphold, support and protect the constitution" as he was sworn into office, 84-year-old Yunus began the tough challenge of returning the country to democracy.

"The number one challenge is the law and order," Touhid Hossain, who has taken over the foreign ministry portfolio, told reporters. "If it is ensured, the rest will be fine."

Hasina, 76, accused of widespread human rights abuses including the jailing of her political opponents, fled by helicopter to neighbouring India on Monday as protesters flooded Dhaka's streets in a dramatic end to her 15-year rule.

The military announced her resignation and then agreed to student demands that Yunus -- who won the Nobel Peace Prize in 2006 for his pioneering microfinancing work -- lead an interim government.

Yunus, who has taken the title of "chief advisor" to the caretaker administration, comprised of fellow civilians bar one retired brigadier-general, has said he wants to hold elections "within a few months".

When polls might take place is not clear.

Officials of Hasina's former ruling party, the Awami League, have gone into hiding after revenge attacks saw some of their offices torched, while former opposition groups such as the key Bangladesh Nationalist Party (BNP) are rebuilding after years of crushing repression.

Several of Yunus' advisers are loosely affiliated with the BNP, led by Hasina's longtime rival and former premier Khaleda Zia, 78, newly released after years of house arrest.

- 'Forge reconciliation' -

Yunus wrote in The Economist this week that his country needed a new generation of leaders "who are not obsessed with settling scores, as too many of our previous governments were".

For Syeda Rizwana Hasan, a top environmental activist and lawyer appointed to oversee climate change affairs, the transition offers a chance to change the country's political course.

"My plan is to lay the foundation to put Bangladesh on a truly liberal democratic path," she said.

That desire for change was echoed by former student leader Nahid Islam, now information adviser in the cabinet.

"This government has been made through a mass uprising, and people have that trust," 26-year-old Islam said.

"Our goal is to reconstruct the Bangladesh that we dreamt in the fastest possible time."

But the new administration faces a daunting task.

Yunus has called for the restoration of order in the South Asian nation after weeks of violence that left at least 455 people dead, calling on citizens to guard each other, including minorities who came under attack.

UN country chief Gwyn Lewis on Friday praised Yunus' "calls for calm and peace", adding she would "work with all parties to forge reconciliation".

- 'Victory day' -

Hasina's flight abroad has heightened rancour towards India, which played a decisive military role in securing Bangladesh's independence, but also backed Hasina to the hilt.

Her son Sajeeb Wazed Joy told the Times of India newspaper his mother still had hope of contesting political office.

"She will go back to Bangladesh the moment the interim government decides to hold an election," he said.

Indian Prime Minister Narendra Modi was among the first to offer his "best wishes" to Yunus on Thursday moments after he was sworn in, saying New Delhi was "committed" to working with neighbouring Dhaka.

India's arch-rival Pakistan on Friday also said it hoped it could boost ties with Dhaka, with Prime Minister Shehbaz Sharif wishing Yunus "great success in guiding Bangladesh towards a harmonious and prosperous future".

China said Friday it also welcomed the interim government, promising to work with the country "to promote exchange and cooperation".

In driving rain, Yunus carried out his first duty as leader, standing silently alongside student and civil society leaders.

Together the group laid a wreath in the red-and-green colours of the national flag at the main memorial commemorating the millions who died in Bangladesh's 1971 liberation war against Pakistan.

Yunus suggested on his arrival in Dhaka on Thursday that Hasina's ouster was as significant as the conflict that brought Bangladesh into being.

"Bangladesh has created a new victory day," he told reporters. "Bangladesh has got a second independence."