Qatar has promised to scrap key elements of its controversial labour laws, in the wake of an international outcry over conditions for migrant workers before the 2022 World Cup, which followed a Guardian investigation into workplace abuse in the Gulf state.

Officials said they would replace the country's "kafala" sponsorship system, which tethers workers to a single employer, who can therefore treat his workforce with impunity, pending the approval of a draft law.

But human rights groups, which had hoped this would be a watershed moment, feared the lack of detailed proposals represented "a missed opportunity to tackle the key issues". Amnesty International said it suspected it amounted to a "change of name rather than a reform to the system".

One significant change is to make it less difficult – though not necessarily easy – for foreigners to leave the country and change jobs. However, altering the rules on "exit visas", which restrict a worker's ability to leave Qatar, and other reforms will have to be ratified by the shura (advisory) council, and businesspeople in Qatar are expected to oppose them vigorously.

"We are going to abolish the kafala system and it will move to the legislative institutions," said Colonel Abdullah Saqr al-Mohannadi, human rights director of the Qatari interior ministry. "It will be replaced by a contractual relationship between employer and employee. We hope that the exit visa will be abolished completely."

The investigative report for which the Guardian won a Webby award

Under the new rules, a Qatari employer would have to show "compelling" proof of any objection to a worker leaving the country. Disputes would be resolved within three days. Other possible changes include mandatory employee welfare contracts, sanctions against employers who fail to meet their obligations, and closer bilateral regulatory links with the workers' countries of origin. Experts say tighter implementation across the board will be the key.

The reforms are based on recommendations by the London law firm DLA Piper, which was commissioned to review the legislative and enforcement framework of Qatari labour laws after the Guardian's investigative reports last autumn. The firm has had a 10-strong team working on the 140-page report for six months.

"This shows willing on the part of the highest levels of government, after a huge amount of international pressure, to reform the kafala system," said a western diplomat. "There will be significant domestic pressure to water down these proposals. Still, things can happen quite quickly if they have the emir's full backing." Sepp Blatter, president of Fifa, which awarded Qatar the 2022 World Cup, claimed it was a "significant step in the right direction for sustainable change in the workers' welfare standards in Qatar".

But Amnesty's James Lynch said: "Promises to fully review sponsorship and exit permits in the long term don't help workers on the ground. The government has been announcing a law on domestic workers' rights since 2008 but we still haven't seen it."

Nicholas McGeehan of Human Rights Watch said: "The notion that the kafala system can be abolished by no longer referring to a 'sponsor' but an employer/employee relationship is utterly preposterous."

Rima Kalush, at Migrant-Rights.Org, said the reforms unveiled amounted to "an announcement of an announcement". "My worry is that Qatar will follow Bahrain's footsteps in renaming the sponsorship system without actually abolishing the majority of the exploitative laws and practices that encompass the system."

More than 85% of the country's total population of 2.1 million are non-Qataris – the highest ratio of migrants to citizens in the world. The largest foreign community is about 500,000 Indians, with large contingents from Pakistan, Nepal, Bangladesh and the Philippines. Qatar, with vast reserves of gas, is officially the world's richest country according to GDP per capita. Doha's many glittering new buildings and massive construction projects are concrete testimony to its immense wealth and ambition.But its construction boom has come at the expense of the safety and wellbeing of many thousands of migrant workers. Investigations by the Guardian, Amnesty International and Human Rights Watch have revealed cases of workers toiling for little pay in unsafe and insanitary conditions. Some have been prevented from leaving the country and others have had their wages withheld. Some end in a kafkaesque nightmare, on the run from the brutality of their official "sponsor", unable to work and so to subsist, unable to leave. Hundreds die.

The International Trade Union Confederation has warned that 4,000 workers could die before a ball is kicked in 2022 if nothing is done to protect their rights.

The DLA Piper report carried confirmation from the Qataris that hundreds of migrants die in the emirate on construction projects each year. The government said 964 workers from Nepal, India and Bangladesh had died while living and working in the Gulf state in 2012 and 2013. A minority of the deaths happened on building sites; in 2012, 246 were recorded as "sudden cardiac death" – the biggest killer among the largest groups of migrant workers in Qatar, according to statistics provided by the state's Supreme Council of Health.

Another 72 were killed in road traffic accidents, and 35 died in falls or by being struck by a "thrown, projected or falling object". In 2012, 28 workers killed themselves by "hanging, strangulation and suffocation and intentional self-harm, by sharp object", the classification states.

Doha still insists no workers have died on World Cup construction projects. Officials like to describe the 2022 Fifa soccer tournament as a "catalyst for change". But DLA Piper warned that increased transparency and communication were crucial.

Changes to the labour laws will be closely scrutinised. The exit visa requirement has already been abolished in the nearby UAE, another huge employer of foreign workers. But an ongoing review is not expected to include agreement to collective bargaining rights.

The fanfare surrounding Wednesday's announcement suggested the Qataris were keen to improve an image that has been tarnished by revelations about migrant labour deaths and conditions.The changes – officially described as "far-reaching labour market reforms" – were announced at a joint ministry of interior and ministry of labour press conference in one of many Doha's luxury hotels, where journalists were welcomed with a groaning buffet before proceedings began. But the speakers were officials rather than ministers – suggesting a lack of confidence in the future of the reform programme.Still, foreigners involved in the migrant labour issue point to improved levels of cooperation. "There's been a change of attitude by the Qataris," said one European legal expert. "They have openly engaged with people. They have allowed themselves to be criticised in their own press. They have some good civil servants but like everyone else they also have some time servers. The scale of the issue is huge."

Shadow international development secretary Jim Murphy, who recently travelled to Qatar, said: "Today's announcement is a small step on a very long journey – and it is absolutely vital that the reforms promised today are implemented quickly and fully. But Fifa must insist that more is done. Football fans will be sickened if the industrial scale exploitation of workers is allowed to continue"

Sharan Burrow, general secretary of the ITUC, was more peremptory.

"Modern slavery will still exist in Qatar despite the announcement of cosmetic reforms to the labour law today. The changes are designed to make it easier for employers to find migrant workers, but the announcement fails to address the multiple violations of international labour standards found by the International Labour Organisation in March. The announcement was made by civil servants and the military, without a government minister present. It gives no guarantee for workers in Qatar."

Further announcements about new legislation and reforms were promised "in the coming months".

• This article was amended on 30 May 2014. The earlier version said "Qatar has an expatriate community of 1.39 million people, which forms more than 85% of the country's total population of 2.1 million". The figure of 1.39 million was given in DLA Piper's review as an estimate of the number of migrant workers in Qatar, but it is thought that there are around 300,000 Qatari citizens, which suggests the number of non-Qataris in the country is around 1.8 million.