premise: Al-Qassam Brigades vowed revenge in a statement.
  A few hours after the incident, a Palestinian was killed and at least two others wounded by Israeli troops' gunfire in the Gaza Strip.
  Monday's violence has cast pall over a visit to the region by US Secretary of State Condoleezza Rice to revive the stalled peace process.
  Israel has stepped up raids and targeted killings of Palestinian militants since a suicide bomb attack killed six Israelis in a seaside city last month.
  The recent worsening of violence has dampened peace hopes ignited by the Israel Gaza withdrawal in September.
   What does the incident refer to?
hypothesis: Israel has stepped up raids