New Delhi, April 23 -- Officers with bomb-sniffing dogs circled cars and searched bags of tourists filing into historic pyramids outside of Mexico City on Wednesday just days after a man opened fire on tourists.

The heightened surveillance was part of a promise by Mexican authorities following the tragedy to beef up security at touristic and archaeological sites across Mexico, less than two months before the country hosts the FIFA World Cup jointly with United States and Canada.

The Monday shooting, carried out by a lone gunman on top of one of the Teotihuacan pyramids - a UNESCO Heritage Site and one of Mexico's most frequented tourist attractions - killed one Canadian tourist and injured a dozen more.

It also set off a flurry of ques...