By Nidal al-Mughrabi, Arafat Barbakh and Tyrone Siu GAZA/ISRAEL-GAZA BORDER (Reuters) -Israeli tanks stormed back into parts of the northern Gaza Strip they had left last week, residents said on Tuesday, reigniting some of the most intense fighting since the New Year when Israel announced it was scaling back its operations there. Massive explosions could be seen over northern areas of Gaza from across the border with Israel – a rarity over the past two weeks after Israel announced a drawdown of forces in the north as part of a transition to smaller, targeted operations. The rattle of gunfire r…