VIENNA (Reuters) -Austria's coalition government has agreed on a plan to enable police to monitor suspects' secure messaging in order to thwart militant attacks, ending what security officials have said is a rare and dangerous blind spot for a European Union country.

Because Austria lacks a legal framework for monitoring messaging services like WhatsApp, its main domestic intelligence service and police rely on allies with far more sweeping powers like Britain and the United States alerting them to chatter about planned attacks and spying.

That kind of tip-off led to police unravelling what they say was a planned attack on a Taylor Swift concert in Vienna, which prompted the cancellation of all three of her planned shows there in August of last year.

"The aim is to make people planning terrorist attacks in Austria feel less secure - and increase everyone else's sense of security," Joerg Leichtfried of the Social Democrats, the junior minister in charge of overseeing the Directorate for State Security and Intelligence (DSN), told a news conference.

"That is why this decision by the cabinet today is an important milestone in the fight against terrorism and spying in Austria," he added.

Under the new system, monitoring of a person's messaging must be approved by a three-judge panel and should only apply to a limited number of cases. Interior Minister Gerhard Karner told the news conference it was only expected to be used on 25-30 people a year.

If it is more than 30, a report must be sent to a parliamentary committee, the government said, addressing concerns about mass surveillance and the infringement of people's privacy.

"The police must have a well-founded suspicion of a possible terror attack" to monitor a person's messaging under the new system, a government statement said.

Once parliament passes the legislation, a tender process for monitoring technology would be launched, and monitoring would begin in 2027, the government said.

(Reporting by Francois Murphy; Editing by Aidan Lewis)