The United States has expressed concern over the disappearance of five anti-extremism activists and bloggers who mysteriously went missing last week, incidents that have triggered an outcry from human right groups. 

Dozens of activists rallied in Karachi for the second time late on Thursday, demanding the five men be accounted for. In Washington, State Department spokesman Mark Toner said the US is taking the disappearances "very seriously" and will "continue to monitor the situation in Pakistan."

Toner also welcomed a statement by interior ministry, which asked police to step up efforts to find the missing.

However, no militant group has so far claimed abducting the activists and no government department or intelligence agency has said it detained or arrested any one of the five.

Activist Syed Talib Abbas said on Friday that none of the missing men have been found so far. Haider's brother Zeeshan Haider said the family had not had any contact with him since he sent a text message to his wife's mobile phone last Friday, asking her to go to a roadside on Islamabad's outskirts and collect his car, which was found there.

Benjamin Ismail, the Asia-Pacific head at Reporters Without Borders, on Friday said the disappearances were "shocking and extremely worrying" and urged authorities to determine the motives and bring those behind them to justice.

-AP