The United States is monitoring the Bangladesh situation "closely" and urges that the formation of an interim government there be democratic and inclusive after Prime Minister Sheikh Hasina resigned and left the country, according to a White House National Security Council spokesperson.

Bangladesh descended into chaos on Tuesday as Prime Minister Hasina fled the country in a military aircraft while the army stepped in to fill the power vacuum after days of anti-government protests that have killed more than 300 people.

"We are monitoring the situation in Bangladesh closely," a White House National Security Council spokesperson said here on Tuesday.

"The United States has long called for respecting democratic rights in Bangladesh, and we urge that the interim government formation be democratic and inclusive," the spokesperson said.

With volatile crowds taking to the streets in Dhaka, Bangladesh Army chief General Waqar-uz-Zaman announced that the 76-year-old prime minister has resigned.

An interim government will be taking over, he said in a televised address. "I'm taking all responsibility (of the country). Please cooperate." The NSC spokesperson said the US "commend the Army for the restraint they have shown today. We encourage all parties to refrain from further violence and restore peace as quickly as possible".

"We express our deep concern and sadness about the reports of casualties and injuries over the weekend and past weeks, and we share our deepest condolences with those who lost loved ones and those who are suffering.

"It will be vital for the new government to carefully and credibly investigate all attacks, and provide accountability and justice for the victims," the spokesperson said.

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