(CNN) The Croatian football federation has blamed "sabotage" after the imprint of a Nazi swastika was left on the pitch used for its national team's Euro 2016 qualifier against Italy Friday night.

The match at the Polijud Stadium in Split was already being played behind closed doors as punishment to the hosts for previous incidents involving its fans, but the few present and viewers on television could clearly see the notorious symbol.

Ground staff made largely unsuccessful efforts at halftime to remove the swastika sign. It was unclear if it had been mowed into the grass or placed there by other means.

The game finished 1-1, to leave Croatia top of Group H by two points from Italy, but it could face further sanction by European governing body UEFA.

Croatia apology

Tomislav Pacak, a spokesman for the home federation, issued a statement about the incident on its official website Saturday.

"We apologize to all viewers, our guests from Italy and the players from both teams, for the Nazi symbol on the Poljud Stadium grass," he said.

"We have immediately notified UEFA of the incident.

"This was an obvious act of sabotage and a criminal act. We condemn it and ask the police and judicial bodies to find the person(s) responsible for what is a shame not only for Croatian football, but the entire country.

"Once again, we express regret and condemn this act, and we apologize to all the viewers, guests and players from both teams."

Pacak claimed that a "chemical agent" had been used on the pitch, 24 to 48 hours before kickoff, timed to be visible during the qualifying match.

The stadium is the home of Croatian top-flight side Hajduk Split.

Previous punishment

UEFA is yet to give its official reaction to the incident, but had ordered the qualifier to be played in an empty stadium as punishment for fan violence and racist incidents when Croatia played Norway earlier in the qualifying campaign.

The crucial top of the table clash had seen Mario Manzukic put the home side ahead after 11 minutes, but Lazio's Antonio Candreva leveled from the penalty spot before halftime for Italy.

The earlier fixture between the two sides in Milan had also ended 1-1 last November and was marred by crowd trouble, with the match temporarily halted after rocket flares were fired on to the San Siro pitch by visiting fans.

Bale heroics

Friday's other major talking point in the Euro qualifying campaign was confined to the pitch, where a fine goal from Real Madrid's Gareth Bale gave Wales an upset 1-0 win over FIFA second-ranked Belgium in Cardiff.

Not going to forget tonight! pic.twitter.com/zM4pH2GyZj — Gareth Bale (@GarethBale11) June 12, 2015

Bale, making his 50th appearance for Wales, scored in the first half and the home side held out against sustained Belgian pressure after the break.

It leaves Wales three points clear of Belgium at the top of Group B and set to qualify for the finals of a major competition for the first time since the World Cup of 1958.

Ronaldo hat-trick

Saturday's qualifying action saw Cristiano Ronaldo score his third successive hat-trick as Portugal edged Armenia 3-2 to consolidate its position on top of Group I.

Brazilian-born midfielder Marcos Pizzelli put Armenia into a shock lead before Ronaldo leveled from the penalty spot and then added two more in the second half. He came into the international off the back of two hat-tricks for his club side Real Madrid.

Portugal hangs on to defeat Armenia, 3-2, thanks to a hat trick from Cristiano Ronaldo. pic.twitter.com/zKL4Ytsj0c — SportsCenter (@SportsCenter) June 13, 2015

Tiago was red-carded for Portugal and the home side grabbed a second through Hrayr Mkoyan, but the group leaders held on for three valuable points.

Robert Lewandowski also scored a hat-trick for Poland as it stayed top of the competitive Group D with a 4-0 home win over Georgia. Remarkably, the Bayern Munich striker was credited with scoring the triple in just the last two minutes of the match as the visitors defense collapsed.

Germany's Andre Schuerrle rounded off the day's hat-tricks as he helped himself to three goals in Germany's 7-0 rout of minnow Gibraltar as the World Cup winners moved to second behind the Poles. Earlier, Scotland drew 1-1 in the Republic of Ireland to boost its hopes of reaching the finals in France.