Israel's Prime Minister has warned of "extreme action" to free a soldier captured by Palestinian militants. Soon afterwards, witnesses reported an air strike on a militant training camp in Gaza, after planes bombed a power station and three bridges overnight. Tanks also moved into the southern Gaza Strip, in the first big incursion since the Israeli withdrawal last year. There are no reports of clashes but the incursion brought condemnation from the main Palestinian factions. Cpl Gilad Shalit was taken prisoner in a raid claimed by three different organisations - including the armed wing of governing party Hamas - after a raid on an Israeli guard post near Gaza on Sunday. Israel last year pulled soldiers and thousands of settlers out of Gaza, which it had first occupied after the 1967 war. In another development, militants in the West Bank showed what they said was a photocopy of the ID card of the 18-year-old Jewish settler Eliahu Asher, whom they claimed to be holding. Mr Asher went missing on Sunday night. The militants have threatened to kill him if Israel continues its operations in Gaza. Witnesses reported that at least one missile was fired into what they said was a Hamas training camp in the southern Gaza town of Rafah. Israel said it had launched an air strike on open fields. There were no immediate reports of casualties. Two Palestinians died in an explosion at a house in Khan Younis in southern Gaza on Wednesday afternoon. But Palestinian security sources told Reuters news agency the blast appeared to be an accident, not part of the Israeli action. Covered by artillery and helicopter gunship fire, the tanks moved in overnight from the Kerem Shalom crossing near southern Gaza, stopping close to Gaza airport.