The former Bangladeshi Prime Minister, Sheikh Hasina, has said that she is determined to return home despite warnings that she will be prevented.
The government says Sheikh Hasina's travel ban is temporary
She told the BBC that "nothing would stop" her from returning to Bangladesh to participate in elections and defend herself against murder charges.
The Home Ministry said earlier that her "provocative and inflammatory speeches" might create civil unrest.
Officials have been told to stop her entering the country.
"My duty is to the people of my country and I owe it to them to fight the election and defend myself against fabricated criminal charges," Sheikh Hasina told the BBC Bengali service.
She said that she would be arriving in London on Thursday with a view to travelling to Dhaka on 23 April.
The government says that Sheikh Hasina, who is on holiday in the US, was responsible for recent street protests that led to a state of emergency.
Another former PM, Khaleda Zia, has reportedly agreed an exile deal.
In a statement, the Home Ministry blamed Sheikh Hasina for issuing "inflammatory statements" against the military-backed caretaker administration and law enforcement forces.
The ministry said her return might create "further confusion and hatred" among the public.
"In the recent past, the civil discipline, security and economy were at stake due to irresponsible and non-stop political agitation and activities led by her party, the Awami League, and other political parties," the statement said.
"And due to this, a state of emergency has to be declared."
The statement said there was "apprehension" that she might jeopardise law and order, and create political instability, endangering public safety and economic life.
"For public safety, the government has issued a special security alert about Sheikh Hasina's return to the country. This arrangement is temporary."
The authorities have placed the police, immigration, air, land and port authorities on alert following their decision.
Sheikh Hasina has been accused of murder and extortion by the military-backed caretaker government.
She has insisted that it has always been her intention to return home to defend herself against what she described earlier this week as "false and fake cases".
Khaleda Zia may go into exile in Saudi Arabia
Sheikh Hasina said on Tuesday that she did not fear detention or physical harm.
"They can do whatever they like, but I know my conscience is clear, I haven't done anything wrong, and I haven't committed any crimes," she said.
"They filed cases and more cases maybe just to punish me."
It was also reported on Tuesday that another former Bangladeshi Prime Minister, Khaleda Zia, had agreed to go into exile in Saudi Arabia with her family.
"She will be leaving the country for Saudi Arabia in a couple of days. Initially she will be leaving with a one-month visa to perform Umrah [a minor pilgrimage to Mecca] and her permanent residence there will be finalised upon reaching the kingdom of Saudi Arabia," the Daily Star reported, citing a senior government source.
"Everything has been finalised... now only the formalities, including getting a visa, remain to be completed," it said.