Scottish independence could put UK security at risk as its enemies could exploit the "uncertainty or distraction" caused by the break-up of Britain, according to the Foreign and Commonwealth Office (FCO).
Scots abroad could also be put at greater risk of "child abduction, forced marriage or crime" through the loss of the UK's consular assistance, the FCO suggested.
It has urged the Scottish Government to provide evidence for its "claims about the status of an independent Scotland, including its membership of international bodies" such as the European Union, the United Nations, Nato, the World Bank and the International Monetary Fund.
The FCO claims to offer "clarity and fact" on the independence process in a submission to the Commons Foreign Affairs Committee released today.
It insists that independence would create "a UK land border" and "harm the Scottish economy" by withdrawing Scotland from the UK's 14,000 treaties and global network of foreign investors.
The FCO said the remainder of the UK would maintain its "strong network of alliances and relationships, and its global foreign policy role", but warned that it is "more difficult to say what the effect (of independence) on the UK's international influence would be".
"Traditional allies may seek reassurance that the UK would retain the ability to project influence and military capability in support of joint objectives and there could be a short-term risk of opponents of the UK's foreign policy seeking to exploit any uncertainty or distraction that could follow a vote in favour of separation for Scotland," the FCO stated.
The FCO submission adds that the loss of coverage from UK consular and trade and investment promotion networks would "have a significant impact on Scottish citizens travelling and working overseas".
"If Scotland was a member of the Commonwealth or EU, the UK, under existing arrangements, could provide some first-line consular assistance to Scottish citizens where Scotland had no diplomatic presence," it stated.
"These arrangements would not extend to those cases that are particularly challenging or sensitive, however, where there is an expectation that assistance would be provided directly by the country concerned. This could have an important impact on Scottish citizens involved in situations such as child abduction, forced marriage or criminal cases in much of the world."