Terrorist attacks and the total number of deaths increased in Bangladesh in 2015, according to the US State Department.

The total number of global terrorist attacks in 2015 fell by 13 percent when compared to 2014, read the 2015 Country Reports on Terrorism prepared by the University of Maryland.

Fatalities as a result of terrorist attacks declined for the first time since 2012 as terrorist attacks decreased by 14 percent, principally as a result of fewer attacks and deaths in Iraq, Pakistan, and Nigeria, three of the five countries worst affected by terrorism, State Department Acting Coordinator for Counterterrorism Justin Siberell said.

More than 28,300 people died - a 14% decline - and about 35,300 others were wounded in 11,774 terrorist attacks worldwide last year, data compiled by the University of Maryland showed.

The State Department said figures showed the terror threat "continued to evolve rapidly in 2015, becoming increasingly decentralised and diffuse".

Extremists were exploiting frustration in countries "where avenues for free and peaceful expression of opinion were blocked", said the press release by the US State Department.

IS was the biggest single threat, the State Department said. The group has attracted affiliates and supporters in the Middle East, Africa and Asia.

Although IS was losing territory in Iraq and Syria, it had gained in strength in Libya and Egypt, the report said.

The report said Iran was the biggest state sponsor of terrorism, saying it supported conflicts in Syria and Iraq, and was also implicated in violent Shia opposition raids in Bahrain.

Bahrain has accused Iran of supplying weapons to Shia militants behind bomb attacks on security forces. Iran denies this.