David Cameron warned a Yes vote in September would result in an "end to devolution" and the start of "irreversible separation".
During a visit to Scotland to make the case for the country remaining in the union, he insisted keeping the group of UK nations together gives them "much more oomph" in the world.
His two-day campaigning trip comes at a time when reports have suggested former Labour chancellor Alistair Darling is being undermined as the leader of the cross-party, pro-UK Better Together campaign.
Mr Cameron, however, said he has every faith in Mr Darling, adding that Better Together is "bringing together an incredibly diverse range of politicians and voices who all share the same vision, that we're better off together as part of the United Kingdom".
With four months to go until the referendum, Mr Cameron added: "It is important that people in Scotland know what the result of this vote is, it is either a vote that separates Scotland from the United Kingdom in an irreversible way, or a vote that reaffirms Scotland's place within the United Kingdom."
His message to voters in Scotland was: "It's very important if you want further devolution, the way to get it is a No vote. A Yes vote is an end to devolution, it's the start of irreversible separation."
The Conservatives, Labour and the Liberal Democrats have all pledged to transfer more powers north if the referendum results in a No vote.
Speaking at Walcheren Barracks in the Maryhill area of Glasgow today, the Prime Minister said: "Voting No to separation, voting to stay in the United Kingdom, can give Scotland the best of both worlds."
"All parties are committed to looking at further devolution, we've already had quite a large act of devolution under this Government. I think Scotland has the choice - voting No with the best of both worlds, having greater say over how Scotland is governed but at the same time being part of a United Kingdom that can make us all stronger, safer, more secure and more successful in this very interconnected world.
"As Prime Minister over the last four years, I made promises about further devolution for Scotland, I think some people might have doubted whether they were going to be fulfilled, but they have absolutely been fulfilled, the Scotland Act is one of the largest acts of devolution that has ever taken place.
"Scotland knows that it has a good level of devolution already and would have the opportunity for more devolution in the event of a No vote, and I think I have demonstrated as Prime Minister across the piece, I have been the Prime Minister who has devolved policing and justice to Northern Ireland, the Prime Minister who has held a referendum in Wales that has seen law-making powers go to Cardiff, that has promised to see another referendum in Wales on tax-raising powers, and that has overseen the Scotland Act and the huge amount of devolution that passes to the Holyrood Parliament.
"So I think I have a track record of showing respect of the nations of the United Kingdom and achieving devolution so that our family of nations can stay together and find a settlement with which all are comfortable."
During his visit, Mr Cameron met some of the servicemen who will be involved in providing security at the Commonwealth Games in the city.
He also argued that keeping the union together would keep the country safer.
The Prime Minister said: "One of the things we have in the United Kingdom is that we have together one of the five top defence budgets in the world. We're building, here in Scotland, two of the most advanced aircraft carriers anywhere in the world.
"Scotland is part of a front rank player when it comes to defence, overseas aid, international diplomacy, a leading member of Nato, a leading member of the European Union, a leading member of the G7 and the G20. Scotland is directly plugged into all these networks with this very powerful and strong defence budget as a key part of it.
"That's a great advantage for Scotland, it's also a great advantage for the rest of the United Kingdom, the United Kingdom benefits hugely from the courage, bravery, expertise and talent of Scots serving in our Armed Forces.
"Of course Scotland could arrange its own armed forces, but think of the benefits of being part of this big organisation that is actually capable of keeping us all safer. Whether in Edinburgh or in London, the threats we face are threats that are global, and our strong and united intelligence services, security services, counter terrorism, the brilliance of GCHQ, our Armed Forces, all those things which we share make us safer.
"I see at first-hand what Britain has together in terms of these resources that can keep us safe, and of course Scotland could have some of those things if it were independent, but think of what we have together and think of how much more oopmh that gives us in the world."
Mr Cameron said he came to Scotland to "campaign and make the arguments strongly and positively for the United Kingdom".
He added: "The decision is to be made by the people of Scotland, but as Prime Minister I passionately believe in our United Kingdom and that we're better off together."
While he said he is "confident in the campaign, confident in its success", he stressed supporters of the union "should take nothing for granted" and "fight very, very hard right up till the last vote is counted".
While SNP politicians have accused some of their unionist counterparts of "talking Scotland down" with their warnings over independence, the Tory leader said he makes no apology for highlighting the "risks of separation".
Mr Cameron said: "I think it would be a dereliction of a politician's duty not to raise those things."
He continued: "I will try and make a strong and positive case, as United Kingdom Prime Minister there are a certain number of arguments I want to put across as clearly as I possibly can.
"I don't have a vote in this referendum but I have a role. I've been encouraging people who don't have a vote that they do have a voice and I want to do that as United Kingdom Prime Minister."
He said that during the referendum campaign, Scottish First Minister Alex Salmond has "come up against some hard truths" on issues such as the currency of an independent Scotland and its membership of the European Union.
"The head of the European Commission has pointed out an independent Scotland would not have automatic access to the EU, it would have to queue up to rejoin," Mr Cameron said.
"What this referendum campaign has done is confronted Alex Salmond with some inconvenient facts that have got in the way of the arguments he was used to making, you've seen that on the currency and you've seen that on the European Union."