1.   In the wake of the incident in Karachi, the U.S. government pondered stiffening a warning to U.S. nationals in the Arab world that was originally issued Monday.

2.   His death prompted the embassy to stiffen a warning against using street taxis in the crime-plagued Mexican capital.

3.   His shooting death prompted the U.S. Embassy to stiffen a warning against using street taxis in the crime-plagued Mexican capital.

4.   His shooting death prompted the embassy to stiffen a warning against using street taxis in the crime-plagued Mexican capital.

5.   Recent robberies of U.S. citizens prompted the embassy to stiffen a warning against using street taxis in the crime-plagued Mexican capital.