Nicola Sturgeon said the authorities cannot be sure there are no other Scots affected.
Poll Shows Labour Support Unchanged
Support for Scottish Labour has not changed since the start of last month, according to a new poll.
The You Gov/Times poll found that support for the party is at 27%, unchanged since the start of February.
Backing for the SNP is at 46%, down two points since the beginning of last month, while it is at 18% for the Conservatives, up three points.
Support for the Lib Dems is unchanged at 4% and for the Greens unchanged at 3%, while Ukip is down two points at 2%.
A Scottish Labour spokesman said: "This is a poll that will be welcomed not only by the SNP but by the Tories. If this is repeated in Scotland on election day then it could help the Tories back into power.
"We need to do everything we can to stop the Tories being the largest party.
"A vote for any party other than Scottish Labour, including the SNP, risks the Tories being the largest party across the UK and David Cameron returning to Downing Street by the back door. That would be a disaster for Scotland.''
The poll of 1,049 people was carried out between March 10 and 12.
SNP Westminster leader Angus Robertson said: "This is another welcome poll - it shows that support to give Scotland a strong voice at Westminster by returning a team of SNP MPs to stand up for Scottish interests remains very high.
"By contrast, Labour support is stuck at the same level it was last October, as they continue to pay the price for being on the same side of so many argument as the Tories.
"We take nothing for granted, and will work extremely hard to win people's trust on 7 May so that we can deliver jobs and growth in place of Westminster cuts, power for Scotland, and the non-renewal of useless and expensive Trident nuclear weapons.''
A spokesman for the Scottish Conservatives said: "This poll shows the Lib Dem vote in Scotland is finished.
"The only real alternative to the SNP pulling the strings of Ed Miliband in Westminster is a vote for the Scottish Conservatives.''
Family members say Laura Macintyre and Eilidh MacLeod haven't been heard from since the explosion.
The families of two girls from the Western Isles missing after attending the concert in Manchester targeted in a terror attack have issued appeals on social media.
Crews were called to the former Royal Victoria Hospital site this afternoon.
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