BRATISLAVA (Reuters) - Europe faces a high risk of more terror attacks because of unchecked migration that has made it easier for attackers and weapons to illegally slip through EU borders, Slovak Prime Minister Robert Fico said on Friday.

Germany and France have both faced Islamist attacks in the past month, and many have blamed German leader Angela Merkel's open-door refugee policy after more than a million migrants came into the EU last year, often fleeing war in Afghanistan, Syria and Iraq. Most headed to Germany.

Although the number of assaults has increased since the migration wave last summer, many of the attackers have been home-grown radicals rather than immigrants.

Fico told a news conference there was an "absolute link between migration and terrorism".

"It is clear that potential terrorists might have used uncontrolled migration not only for passage but also to bring weapons and explosives," he said. "Therefore the probability there might be more individual terror attacks is very high because there is potential for such attacks."

Slovakia has been one of the toughest critics of the European Union's response to the migration crisis, opposing quotas for asylum seekers and calling for beefed up borders.

It has promised to be an "honest broker" while holding the bloc's rotating presidency for the rest of the year.

Fico said some security experts estimated there are around 300,000 migrants in Europe, the bulk of them in Germany, whose backgrounds and intentions were unknown to security officials.

"Anyone could have crossed the borders during the huge influx of illegal migrants. God knows what they had in their backpacks beside food and clothes," Fico said.

(Reporting by Tatiana Jancarikova; Writing by Jason Hovet; Editing by Tom Heneghan)