UPDATE 1-Belgium's Mobistar sees margins shrink in first quarter
* Core profit margins fall to 29.7 pct from 31.5 pct
* Repeats 2013 core profit, turnover targets
* Fixed-line customer base falls sharply (Adds details, background)
BRUSSELS, April 22 (Reuters) - Belgian telecoms group Mobistar said that regulatory caps on calls abroad and within Belgium had eaten into its profit margins in the first quarter, with its fixed line business continuing to struggle.
Mobistar, which had 4.45 million customers in Belgium and Luxembourg at the end of the first quarter, said its profit margins had fallen to 29.7 percent from 31.5 percent in the first three months of 2012.
Mobistar said the number of customers increased from a year earlier. However, this was solely due to people taking up services from other providers, such as rival Telenet which used Mobistar's mobile network. Excluding these, customer numbers fell.
The group said it would introduce new fixed-line products, such as TV and broadband, as soon as the regulator forced competitors, such as Telenet, to open up their networks.
The fixed-line business constitutes only a small part of the group's revenues and has been difficult to improve. Mobistar's current TV is broadcast via satellite and broadband via former state monopoly Belgacom.
The group repeated its outlook for a 2013 core profit between 380 and 420 million euros and turnover to decline between 4 to 6 percent.
It also said that from 2014 onwards it would increase its cost savings target to 50 million euros from 30 million earlier.
Core profit (EBITDA) for the first quarter of 2013 fell 12.7 percent to 98.7 million euros ($129.11 million), slightly above the 97.1 million expected in a Reuters poll of five analysts. ($1 = 0.7644 euros) (Reporting by Robert-Jan Bartunek; editing by Philip Blenkinsop)