Why should Israel lift the seige? To let terrorists pass into Israel, or to let Hamas bring in more weapons? Israel already allows food, medicine, etc. to go in. I suppose you think that Hamas' policy of genocide (read their charter) is within the law? Under the circumstances, Israel's actions are right, proper and legal.
Boko Haram extremists kill 26, including children (AP)
from the article: Year after Gaza war, Hamas says ready to fight Israel again