Gaza’s sole power plant will have to shut down within 48 hours if a strengthening of the blockade imposed on the Strip by Israel is not ended, officials warned on Thursday, as border tensions simmered following the arrest of a Palestinian militant leader. Israeli authorities have closed all crossings into Gaza, cutting off access for the fuel trucks that supply the plant, over fears of retaliation attacks following Monday’s arrest of Bassam Al-Saadi, a senior leader of the Palestinian Islamic Jihad group. The restrictions are an intensification of a siege that has been in place since 2007. The…