Amnesty International has expressed deep concern for Bangladesh's minority Muslim Ahmadiyya community.
About 5,000 people rallied against Ahmadis in Dhaka in January
It says some Islamic groups have threatened to step up attacks on Ahmadi places of worship.
The Ahmadis, who number 100,000 in Bangladesh, do not believe Mohammed was necessarily the last prophet.
Amnesty called on the government to condemn any acts of violence and to ensure members of the Ahmadiyya community were protected.
"The government of Bangladesh must take decisive action against anti-Ahmadi agitators who have continued to attack members of the Ahmadiyya community," Amnesty said in a statement.
"These groups have been allowed to attack Ahmadis with impunity."
The group said 11 Ahmadis were seriously hurt in an attack in Brahmanbaria, 75km (47 miles) north-east of Dhaka, last Friday and that Islamist groups had threatened to carry out attacks more frequently.
Amnesty called for an independent investigation into the attack in Brahmanbaria.
The government could not be reached for comment on Friday.
In January, the government banned publications by the Ahmadiyya movement as a 5,000-strong rally marched to an Ahmadiyya mosque in Dhaka to denounce the movement.
A home ministry statement said the ban "was imposed in view of objectionable materials in such publications that hurt or might hurt the sentiments of the majority Muslim population of Bangladesh".