The systematic persecution and murder of foreign nationals in Ivory Coast has been revealed in a harrowing eyewitness account obtained by human rights monitors.

A 21-year-old Malian man told Human Rights Watch how he and six other west Africans were forced to their knees in a dark basement and beaten with an iron bar. Five of the men were executed at point-blank range but he resisted and escaped.

The watchdog said it had documented the beating or burning to death of at least 14 west African immigrants in Ivory Coast. Its report chronicles rising atrocities on both sides of the country's political divide and said those committed by president Laurent Gbagbo's forces may constitute crimes against humanity.

The Malian national, who was not named, told the NGO how he narrowly avoided death on 6 March when he and six others were abducted and forced into two vehicles by militiamen.

"That day I was wearing dirty clothes from working as a porter," the man was quoted as saying. "That's how they knew I was Malian – we're most of the porters. As I was walking, six guys with Kalashnikovs came up behind me, and one of them stuck it into my back and pushed me toward the road. They did the same thing to a couple of others, and soon they had seven of us in total.

"We were all west African nationals. They forced us into two taxis, and when we arrived at an unfinished house they forced us to go down to a basement, where there were other guys with Kalashes waiting. It was dark down there, so they used their cellphones for lights to take us down. It smelled horrible."

He continued: "They beat us with an iron bar and a belt that had a sharp metal buckle. Four of them stood at guard with guns pointed on us at all times. All of them in the basement wore balaclavas. Then they attached black bandanas over the eyes of the first two guys, and one of the [pro-Gbagbo Young] Patriots executed [them] at point-blank range.

"Another guy was lighting the area for him with a cellphone to make sure he didn't miss, even though the distance was only two metres. They did the same to the next three guys, as they were begging for their lives. Five executed right next to me, as they were on their knees. The whole time they kept saying we were rebels, we were rebels.

"When they tried to put the bandana on my head, I fought back. Every time they tried, I'd fight. So then they again beat me with the iron bar. I kept refusing to let them put the bandana on, as did the guy next to me, a youth from Niger. Eventually I heard them say they would finish us off elsewhere, and they took us back outside."

The man concluded: "They forced the guy into a taxi, but I saw another car coming and I took the chance to run for it. They fired two gunshots from behind, but didn't hit me. I ran and then once I got out of their sight, I found a spot to hide. Eventually I made it back home."

Ivory Coast has been locked in violent turmoil since a disputed November election between Gbagbo and his rival Alassane Ouattara, widely recognised as the winner.

Human Rights Watch described an organised pattern of xenophobic attacks. It said the homes, shops and mosques of hundreds of west Africans have been burned, and many have been chased out of their neighbourhoods under threat of death at the hands of pro-Gbagbo militias.

The majority of these attacks came immediately after Gbagbo's youth minister, Charles Ble Goude, called for "real" Ivorians to set up roadblocks in their neighbourhoods and "denounce" foreigners. A militant pro-Gbagbo group has warned Burkina Faso nationals to leave the country by 22 March.

Witnesses described to the watchdog how west Africans were killed by militiamen after being pulled out of taxis. Two marketplace porters were tied up, stuffed into their handcarts and set ablaze. A handicapped man from Burkina Faso accused by militiamen of hiding rebels in his house was brought into an abandoned building and set on fire. Attackers amputated the penises of two other men, then killed them.

The report said: "Residents from Mali, Burkina Faso, Nigeria, and Niger gave detailed accounts of daily attacks by pro-Gbagbo security forces and armed militias, who beat foreign residents to death with bricks, clubs, and sticks, or doused them with gas and burned them alive."

Human Rights Watch also documented the rape of nine women by groups of militiamen and police operating together; all the victims were active and public members of Ouattara's political party. In two cases, the women were raped in front of family members, and the husband and father of the victims were then arbitrarily detained and remain "disappeared", the group said.

The report detailed how victims of political violence have been beaten to death with clubs, large pieces of concrete, knives, axes and machetes. Others had their throats slit or were doused with petrol and set ablaze.

It criticised gunmen claiming allegiance to Ouattara – who have taken over parts of north Abidjan in the past three weeks – for summary executions of 11 pro-Gbagbo troops captured since they rose up against the incumbent.

Daniel Bekele, Africa director at Human Rights Watch, said: "The time is long overdue for the UN security council to impose sanctions against Gbagbo and his allies directly implicated in the grave abuses of the post-election period. The international community should also send a clear message to Ouattara's camp that reprisal killings will place them next on the list."