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The centre-right ruling coalition, which faces an election this year, agreed with the anti-immigration Danish People's Party in May to beef up border controls, saying it aimed to keep "brutal crime" out of Denmark.
But the plan brought a warning from the European Commission that Denmark risked contravening the Schengen treaty governing free movement in Europe's 25-nation passport-free Schengen area and criticism from neighbouring Germany.
In the face of such criticism, the Danish government has insisted that it is within its rights to step up customs controls aimed at stopping smuggling of illegal goods such as weapons and narcotics and trafficking of people.
It says it is only raising its customs force to a level similar to that of its neighbours, Germany to the south and Sweden to the north, and that the measures will not hinder traffic and do not involve reinstating passport controls.
It says customs officers will only carry out random checks, as they have previously, and there will not be any systematic control of all vehicles and trains passing the border.
On Tuesday, 50 additional customs agents, 30 of them on the Danish-German frontier, 10 at ferry terminals with service to and from Germany, and 10 at the Oresund bridge and Helsingor ferry dock linking Denmark to Sweden, were scheduled to take up their positions.
The reinforcements at the bridge to Sweden were due to begin working around 9:00 a.m. local time (8:00 a.m. British time) and those at the border with Germany at 10:00 a.m. local time, a customs administration spokeswoman said.
The reinforcements come on top of a force of about 160, which will grow to 260 by the end of this year.
Announcing the deal with the Danish People's Party in May, Finance Minister Claus Hjort Frederiksen said: "We have seen too many examples of violence, break-ins and brutal criminality committed by perpetrators who have crossed the borders."
Lawmakers cleared the way and granted the funding for the measures on Friday.
Denmark will assume the EU's rotating presidency from 1 January 2012.
EurActiv with Reuters