EU antitrust regulators will this week warn Norwegian telecoms company Telenor and Sweden's TeliaSonera about the adverse impact of their plan to combine forces in Denmark, two people familiar with the matter said on Monday. Telenor and TeliaSonera are seeking to boost margins in their toughest market by merging their Danish mobile activities, allowing them to better compete with former incumbent TDC and Hutchison Whampoa's majority owned Hi3G.