Regime accused of holding 2,918 people in secret, while thousands of others are forced to flee

A sweep by government forces has seized one person every hour during the five-month Syrian uprising and detained them in secret, leaving their families no way to locate them, says a human rights group.

The group, Avaaz, claims 2,918 people have been "forcibly disappeared" since anti-government demonstrations began in Syria on 15 March. Most are accused of being involved in the rebellion that continues to undermine a regime long renowned as the Middle East's most formidable police state.

An additional 12,617 people also remain in detention; however their incarceration has been declared to family members. Tens of thousands more people have fled from towns and villages in northern Syria in the face of intensive military assaults that Damascus claims are ridding the area of criminals and collaborators.

The scale of the detentions in Syria has been compiled by a network of activists and researchers who have provided information to Avaaz. The group has gathered photos of many of the disappeared and is launching an awareness campaign today.

"Hour by hour, peaceful protesters are plucked from crowds by Syria's infamously brutal security forces, never to be seen again," said Avaaz's executive director, Ricken Patel. "President Assad's attempt to terrorise Syrians into submission isn't working, but they urgently need the international community to demand the release of the disappeared and a transition to democracy."

One young Syrian professional spoke to the Guardian about the disappearance of her father, who vanished from a Damascus suburb on 2 July. "My father used to talk a lot," she said, declining to reveal her name. "He talked against the government in a political way. We used to tell him to stay quiet but he wouldn't listen.

"They came to a neighbour's fast food shop and they took him. We haven't heard anything from him since. They don't even acknowledge that they have him."

She said security officials had come looking for her at her university, in what she suspects was an attempt to place further pressure on her family. "It is unimaginable not knowing what has happened," she said. "The fear is worse than the intimidation. That is their weapon."

A second man, Udai al-Sayed, who worked in a media production company in Idlib before fleeing to Turkey, said his brother, Moustafa, was taken on 12 June.

"The accusation against him was that he had more than one Syrian mobile number registered in his name," Sayed said. "It has been impossible to find out anything about him, although we heard a rumour that he escaped prison but his hands and feet may have been broken."

The brothers had regularly turned out for protests in Syria's rebellious north, where the military has had an especially strong presence over the past three months. Officials in Damascus claim the country's military is combating a Sunni Islamist uprising bent on stirring sectarian war in Syria.

"I participated in all the protests before I left," said Sayed. "And I saw all components of Syrian society, Christians, Muslims, Kurds uniting as one to demand their rights. The government and the army is sectarian, not us.

"They are killing and detaining in a very cruel way. People have kneeled to Assad for 42 years. They need to understand that Syria is not a farm that belongs to Assad and his family. It is a free Arab country and the people will take their rights."

Avaaz's research, together with separate reports and videos coming out of Syria show its citizens are paying a particularly high price for their dissent. At least 1,600 demonstrators have been killed since the uprising began. The government claims that more than 300 members of the security forces have also been killed.

The government is actively working to prevent outside scrutiny of the uprising, limiting the number of foreign reporters allowed into the country and strictly supervising those that are.

However, visitors who have got in bear witness to a country under full military occupation, with all military units actively deployed throughout the country.

Military intelligence agencies are playing a lead role in the secret detentions, according to multiple sources inside Syria and in Turkey, which continues to provide refuge to many who have fled.

The sweeps are thought to have intensified over the past week in the lead-up to the Muslim Holy Month of Ramadan, which begins next week.