Houthi fighters ride a patrol vehicle in Sanaa. As demonstrations grow, Houthis are detaining and beating peaceful protesters. (Khaled Abdullah/Reuters)

The Houthi rebels who have seized control of northern Yemen are systematically targeting peaceful protesters in the capital with death threats, abductions and severe beatings, according to activists and human rights groups.

The increasingly brutal tactics, they say, are meant to halt demonstrations that erupted ­after the Houthis toppled Yemen’s pro-American government in Sanaa last month and then dissolved parliament. But the knifings and other violent measures appear to be having the opposite effect. Rallies against the Houthis have increased in frequency and size, heightening concerns that the country is heading for all-out civil war.

Several Yemenis said in interviews that they or their friends had been unlawfully detained and abused by Houthis. At least one protester, identified as Salah al-Bashri, died as a result of what appeared to be beatings he suffered while in Houthi custody, according to an ­Amnesty International report released Monday.

The instability in this ­Arabian Peninsula nation has prompted most Western governments to close their embassies and has led U.S. authorities to scale back counterterrorism operations here. Washington had previously worked closely with Yemeni authorities to combat al-Qaeda’s most dangerous affiliate, ­al-Qaeda in the Arabian Peninsula, which is based here. The United States and other Western powers have not recognized the Houthis as the new government.

The Houthis, who are followers of the Zaydi branch of Shiite Islam and have been in rebellion against the government for years, captured the capital of this majority Sunni country in September and took effective control of the military, police and judiciary.

Now the rebels are using those institutions to persecute their critics, according to ­human rights organizations and participants in demonstrations.

Ahmed al-Thubhani, 21, said he was arrested by Houthis in police and military uniforms as he left an anti-Houthi demonstration Feb. 7 at Sanaa University. He was detained at a residence for five days, he said, where Houthi militiamen struck his legs, back and forearms with a wooden stick, threatened to kill him and forced him to confess to spying for the CIA.

His abductors also forced him to give names of other protesters, he said. “They said they would kill me if I didn’t do what they said,” Thubhani said.

Deif Allah al-Shami, a senior Houthi leader, denied that the rebels were beating protesters at unofficial detention centers or unleashing unprovoked violence during demonstrations.

“This is not our style. We have morals and ethics, and everyone knows that Ansarullah are ­honest and do not use such methods,” he said, using ­another term for the Houthis.

Shami added that the Houthis have formed a committee to investigate the killing of Bashri, although he did not give further details. The Amnesty International report said that Bashri, a 35-year-old father of seven, was subjected to “hours of torture” along with two other men after they were detained Feb. 11 at a demonstration in Sanaa.

Evidence of abuse

Yemen has long had a poor human rights record, according to advocacy groups. Security forces brutally suppressed protests in 2011 calling for the removal of longtime ruler Ali Abdullah Saleh. His successor, President Abed Rabbo Mansour Hadi, was seen as having a better record, but his government came under criticism last year when security forces shot and killed at least six protesters in Sanaa.

Escalating violence in Yemen has analysts, diplomats and many Yemenis worried. Here's what led to it, and why you should care. (Gillian Brockell/The Washington Post)

Human rights groups and ­activists say there is growing evidence of abuse by the Houthis.

“Testimonies reveal how protesters have been detained and tortured for days on end. The safety of all those who dare to speak out against the Houthi rule is on the line,” Donatella Rovera, a senior crisis response adviser at Amnesty International, said in the group’s report. She added that the Houthis have “stooped to a dangerous new level of intimidation and violence to strike fear into anyone protesting their rule.”

Baraa Shiban, a Yemeni ­human rights coordinator for Reprieve, a British nonprofit, said protesters are regularly taken to unofficial detention centers, such as private homes and empty buildings, and interrogated without charges or access to a lawyer. Shiban said he has documented 57 unlawful detentions in the capital since late January. The actual number is probably much higher, he said, but many victims fear Houthi retaliation if they report abuses.

The Houthis wear police or military uniforms “to make it seem like they’re not part of a militia, like what they’re doing is somehow sanctioned by state institutions,” he said.

Activists and rights groups say they have received similar reports of abuses against protesters in other areas of Yemen that are under Houthi control. But they have been unable to document them, they say, because of restrictions by the insurgent group, a volatile security situation and a lack of resources.

Female activists threatened

In a forthcoming report, Human Rights Watch cites the detention of at least 46 male protesters by armed men, both uniformed and in civilian clothing, in Sanaa between Jan. 25 and Feb. 11. The report notes that at least three protesters appear to have been tortured while in custody.

At demonstrations, the report says, law enforcement officers have fired live rounds into crowds at least three times. It adds that the uniformed men have been observed hoisting placards with Houthi slogans as well as images of the group’s leader, Abdulmalik al-Houthi.

Afif al-Mansani, 33, an ­accountant who has protested the Houthi takeover, said men in uniform and civilian attire act in tandem, beating demonstrators with rifle butts and attacking them with knives. He added that one of his friends was stabbed at a rally this month.

“There’s no difference ­between those that wear uniforms and those who don’t. They are nothing but thugs,” he said.

Samia al-Aghbari, 33, an ­activist who was prominent at the protests in 2011 that led to the ouster of Saleh, said she and other female activists have ­received death threats. She said she has been harassed by Houthi loyalists on Facebook and has received a torrent of messages accusing her of sexual indecency.

“I recently received a message from someone who said that if I dared to criticize Abdulmalik al-Houthi, he’d cut out my tongue,” she said, adding that she has begun to fully cover her face because of concern over being targeted by Houthi militiamen.

“We know they’re watching us, wanting to abduct us,” she said.