SAO PAULO (REUTERS) - Police in the Brazilian state of Mato Grosso are investigating the alleged attempted rape of an American woman on Friday night in the city that hosted the World Cup football match between Australia and Chile.

The woman, 24, was accompanied by US Embassy officials to a hospital in the state capital, Cuiaba, a statement from the Mato Grosso state civil police said on Saturday, the third day of the month-long tournament.

A medical exam found later that rape had not actually been committed and police were waiting on additional tests, according to a second report from public security officials.

The woman and her boyfriend were staying in the home of someone they met during Friday's World Cup celebrations and she woke up screaming with a man on top of her, the police statement said.

Several people were interviewed about the incident, including the owner of the home, but no one has been arrested.

A US Embassy spokesman in Brasilia said the embassy was aware of reports of the case but could not comment due to privacy laws.

Cuiaba, in central Brazil, usually sees few tourists, but will host three more games: on Tuesday, between Russia and South Korea; on June 21, between Nigeria and Bosnia; and on June 24, between Japan and Colombia.

Brazil has taken pains to ramp up security during the World Cup, with about 100,000 police patrolling the 12 host cities complemented by nearly 60,000 soldiers.

The tournament has gone more smoothly than many expected, but there have been reports of robberies in several host cities, including 12 cases involving tourists registered by police in Cuiaba on Friday.

The rape and kidnapping of a foreign student in host city Rio de Janeiro in April shocked residents and raised concerns about World Cup security.