Selam hoped that escaping from Eritrea into Sudan would be the first step towards a better life for her unborn child, away from military service and dire economic prospects.

But after traffickers seized her in Sudan, the dream quickly became a nightmare. Selam -- not her real name -- was beaten, raped and shot in captivity.

Despite her ordeal, two years later she set out again, joining thousands of migrants from Eritrea, Ethiopia and Somalia willing to risk anything to reach Europe.

"I suffered every kind of abuse a woman can face," the 32-year-old said, speaking in the Khartoum office of the UN refugee agency (UNHCR).

Nearly 30,000 Eritreans and Ethiopians crossed the Mediterranean from North Africa to Italy last year, as did smaller numbers of Somalis and Sudanese. Almost all travelled via Sudan, the UN says.

"Everyone comes, whether there are risks or not," Selam said, her three-year-old son clutching her side.

Crossing Sudan's porous eastern borders, most migrants go to Khartoum where they pay smugglers to take them thousands of kilometres (miles) to the Libyan coast to chance a perilous sea crossing.

Last year the journey cost some 3,800 migrants their lives.

Selam never reached Libya, and her experiences traumatised her deeply.

In April 2012, she was entering her seventh year as a conscript -- military service can last indefinitely in Eritrea -- when she found she was three months pregnant.

She made up her mind to flee to Sudan immediately and decide where she could then go to raise her child.

On leave that month, she took the bus to the border and walked unchallenged into eastern Sudan.

- Raped, beaten and shot -

As she traipsed through arid scrub outside the city of Kassala, two pick-ups armed with machine guns appeared and pulled up besides her.

She was forced to get in.

The men in the trucks -- Selam says they were Arab tribesmen from eastern Sudan -- were people traffickers.

She was taken first to a safe house and then to Egypt's Sinai, an arduous two-week drive in searing desert heat.

"On the way there was a lot of abuse. We were badly treated," she said.

Far worse was to come, as she and 22 other Eritreans were sold to a Bedouin gang.

For seven months, her captors raped and beat her, keeping her in squalid conditions as they called Selam's family and members of the diaspora in Europe to demand $30,000 for her release.

"To bring them money, we were beaten every time we made the calls," she said.

Months before she gave birth that September, she tried to escape but was caught and shot in the ankle.

Lifting the hem of her robes, she pointed to a raised, shiny scar on her ankle. Walking still causes her pain.

Only when members of the Eritrean diaspora raised $15,000 was she dumped near Egypt's border with Israel, where troops detained her.

She was deported to Asmara three months later and jailed for six months for leaving Eritrea illegally.

Fearing further reprisals for desertion, Selam already knew she would leave again.

Between her first journey and her return to Sudan in 2014, Khartoum worked to tackle the trafficking.

- The Khartoum Process -

"Sudan is fighting human trafficking in a number of ways. Firstly with Sudanese law that forbids this crime and punishes it, and the government has set up specialised prosecutors for the crime," Sudan's commissioner for refugees Hamed al-Gizouli told AFP.

In 2014, Sudan also joined an initiative with the European Union and other east African countries -- the Khartoum Process -- to coordinate a response to migration in the region.

With no official figures for migrants trafficked in Sudan, it is difficult to gauge how successful such measures have been.

The International Organization for Migration says Sudan has made progress, but challenges remain.

"The difficulties that Sudan is facing are the length of its borders with the neighbouring states," IOM Sudan head Mario Lito Malanca told AFP.

Other challenges include the changing routes migrants follow, and the international nature of trafficking networks.

When Selam was released from prison she again set about planning her departure and began her second journey in early 2014.

This time she reached Khartoum, where the Eritrean community gave her accommodation before she sought help from the UN last September.

Selam's motives for leaving Eritrea were commonplace.

"The root cause of course is underdevelopment, it is poverty, it is unemployment," said UNHCR's Sudan head Mohamed Adar.

"It is something that requires a much more comprehensive approach."

After nearly two years in Khartoum, Selam didn't want to reveal too much about her plans, although her goal remains the same as four years ago.

"I'd like to go anywhere I could receive medical treatment and raise my child," she said quietly.