Israel has re-arrested 51 Palestinians freed in a prisoner swap deal three years ago.

The army said it was part of its hunt for three missing Israeli teenagers, believed to have been abducted in the occupied West Bank.

Meanwhile Israeli human rights group B’Tselem has accused Israel of imposing unlawful collective punishment on Palestinians in Hebron after it closed off all entrances to the city and banned people from travelling.

The two 16 year olds and one 19 year old disappeared on Thursday.

Thousands of Israeli soldiers have been deployed to the area to look for them. One Palestinian has been killed and around 200 detained since the operation began.

Palestinian President Mahmoud Abbas has demanded the release of the three youngsters and said his forces are also searching for them.

Israel said on Wednesday it had approved the construction of 172 new homes for Jewish settlers in annexed east Jerusalem.

The U.N. Security Council deems settlements built on territory captured in the 1967 war illegal. The US also regards them as “illegitimate.”