Blatter on Friday acknowledged concerns but saying the football union could not step in.
"Fifa cannot interfere with the labour rights of any country, but we cannot ignore them", Blatter said on his Twitter account @SeppBlatter after Fifa wrapped up a crunch two-day meeting behind closed doors at its Zurich base.
The tweet marked his first public comments on the storm raging since a report by Britain's Guardian newspaper last week.
The global football governing body's 2010 decision to name Qatar to host the 2022 edition of the international game's showcase tournament has been dogged by controversy from the outset.
Even before renewed claims that migrant labourers in wealthy Qatar are treated like slaves – and paying with their lives – Thursday and Friday's session of Fifa's executive committee had been expected to focus heavily on Qatar.
Controversy is raging over the idea of shifting the tournament from the World Cup's traditional June and July slot to escape the scorching Gulf heat – a climate issue critics say should have been self-evident from the outset.
European leagues are up in arms, saying such a move would cause havoc to their fixtures, while winter sports federations and broadcasters argue that a high-profile football event in the middle of their own seasons would dent television audiences and revenues.
Addressing that issue, Blatter tweeted that the executive committee had "decided to launch a consultation process among main stakeholders for Qatar 2022 dates" and that no decision would be taken before the 2014 World Cup in Brazil.
Outside the world of football, the "winter versus summer" debate has been overshadowed by the controversy over the treatment of workers in Qatar.
Gulf nations have frequently faced criticism over their rules on migrant workers and the treatment they face, but the fact that the latest claims are linked to the World Cup has put the issue centre stage.
The Guardian, quoting documents from Nepal's embassy in Qatar, said thousands of Nepalese – at 370 000 the second largest group of labourers in the oil- and gas-rich kingdom after Indians – faced "modern-day slavery" and that dozens had died in recent weeks.
According to the International Trade Union Confederation, which raised the alarm in August and is sending a delegation to Qatar next week, if current death-rates continue, at least 4 000 workers could perish before the 2022 World Cup even begins.
Beyond the fatalities, critics also slam the confiscation of passports, withholding wages for long periods, debts to recruiters, insufficient drinking water in high temperatures, and squalid camps for labourers.
Amnesty International is set to publish an in-depth report next month on Qatar.
"The combination of forms of exploitation in certain cases that we have documented, we would consider that to amount to forced labour," James Lynch, Amnesty's researcher on foreign workers in the Gulf, told AFP.
Qatar repeatedly has rejected claims that conditions on the emirate's construction sites can be tantamount to forced labour.
It says it takes its international commitments seriously, and has announced plans to double its number of labour inspectors to 150, though critics question the likely effectiveness of that.
Arriving on Thursday at Fifa, Hassan Al Thawadi, head of Qatar's World Cup committee, said worker deaths were a stark issue and insisted the government was dealing with it.
"Is this acceptable? Of course it isn't. The government has said so quite clearly," he told reporters.
"We are going to ensure the security, the protection and the honour of everyone. We've worked to that pledge, will continue to do so, and will always give it the utmost priority," he added.
Qatar's critics acknowledge that construction-site deaths can occur anywhere in the world, but say the issue is particularly shocking in Qatar, the world's wealthiest nation per capita.
Pressed on the issue on Thursday, Fifa communications chief Walter De Gregorio said: "Any death is a death too many."
"Together, I think, we're going to find a solution to improve, or maybe to change, the situation that for sure, for everybody, is unacceptable," he said.
"But I want to highlight that it's not Fifa against Qatar. We're all on the same page, trying to change the situation for the better of everyone. Qatar can change, and Qatar is very open to all discussions we're having," he added. – AFP