* U.N. Security Council to meet on Tuesday

* Biden calls for “whole of government” response

* Suu Kyi’s whereabouts not known

* Junta replaces key ministers

The United States threatened to reimpose sanctions on Myanmar’s generals after they seized power and arrested Suu Kyi and dozens of her allies in dawn raids on Monday.

The Nobel Peace laureate’s whereabouts remained unknown more than 24 hours after her arrest and her only communication has come in the form of a statement written in anticipation of the coup calling for protests against military dictatorship.

The U.N. Security Council was due to meet later on Tuesday, diplomats said, amid calls for a strong global response to the military’s latest seizure of power in a country blighted for decades by army rule.

The coup followed a landslide win for Suu Kyi’s National League for Democracy (NLD) in Nov. 8 elections, a result the military has refused to accept citing unsubstantiated allegations of fraud.

The army handed power to its commander, General Min Aung Hlaing, and imposed a state of emergency for a year, crushing hopes the poverty-stricken country also known as Burma was on the path to stable democracy.

The NLD’s executive committee demanded the release of all detainees “as soon as possible”.

In a post on the Facebook page of senior party official May Win Myint, the committee also called for the military to acknowledge the election results and for the new parliament to be allowed to sit. It has been due to meet on Monday for the first time since the election.

U.S. President Joe Biden called the crisis a direct assault on Myanmar’s transition to democracy and the rule of law, and said his administration would watch how other countries responded.

“We will work with our partners throughout the region and the world to support the restoration of democracy and the rule of law, as well as to hold accountable those responsible for overturning Burma’s democratic transition,” Biden said in a statement.

The crisis is one of the first major tests of Biden’s pledge to collaborate more with allies on international challenges, especially on China’s growing influence.

The United Nations led condemnation of the coup and calls for the release of detainees, in comments largely echoed by Australia, the European Union, India and Japan.

‘WORRY FOR THE FUTURE’

China did not join the condemnation, saying only that it noted the events and called on all sides to respect the constitution. Other countries in the region including neighbouring Thailand declined to comment on Myanmar’s “internal affairs”.

The streets of Myanmar were quiet overnight during a curfew already in place to stop the coronavirus. Troops and riot police took up positions in the capital, Naypyitaw, and the main commercial centre, Yangon.

In one of the first callss for specific action to oppose the coup came from the Yangon Youth Network, one of Myanmar’s biggest activist groups.

“Yangon Youth Network … declared and urged CD (civil disobedience) as an immediate response,” a representative said on Twitter, noting that doctors at a hospital in the city of Mandalay had also begun a similar campaign.

China’s state Xinhua news agency quoted a military official as saying most regional and state leaders who were detained during the takeover were released on Tuesday,

The chief minister of the Sagaing region, Myint Naing, told the BBC after his release that he had been kept in a dormitory and treated well.

“I worry for the future of the nation. We hoped for the best but the worst is happening,” he said.

By Tuesday morning, phone and internet connections were restored but usually bustling markets were quiet and Yangon’s airport was closed.

Banks in Yangon reopened after halting services on Monday due to poor internet connections and amid a rush to withdraw cash.

Citizens feared upheaval would further hurt an economy already reeling from the COVID-19 outbreak.

“People aren’t going out,” said taxi driver Aung Than Tun.

LONG STRUGGLE

Suu Kyi, 75, endured about 15 years of house arrest between 1989 and 2010 as she led a democracy movement against the military, which has ruled for much of the past six decades.

The latest coup marks the second time the military has refused to recognise a landslide election win for the NLD, having also rejected the result of 1990 polls that were meant to pave the way for multi-party government.

Following mass protests led by Buddhist monks in 2007, the generals set a course for compromise, while never relinquishing ultimate control.

The NLD came to power after a 2015 election under a constitution that guarantees the military a major role in government, including several main ministries, and an effective veto on constitutional reform.

Consolidating its position, the new junta removed 24 ministers and named 11 replacements for various portfolios including finance, defence, foreign affairs and interior.

Military chief Min Aung Hlaing has promised a free and fair election and a handover of power to the winner but without giving a timeframe.

Buddhist monk Shwe Nya War Sayadawa, known for his support for the NLD, was also among those arrested on Monday, his temple said. Monks can be a powerful political force in Buddhist-majority Myanmar.

One of the main concerns for UN diplomats is the fate of Rohingya Muslims who have endured years of harsh treatment at the hands of the military.

A 2017 military crackdown in Myanmar’s Rakhine State sent more than 700,000 Rohingya Muslims fleeing into Bangladesh.

About 600,000 Rohingya remain in Myanmar, including 120,000 people who are effectively confined to camps.

(Reporting by Reuters staff Writing by Stephen Coates, Robert Birsel Editing by Lincoln Feast & Simon Cameron-Moore)