TEL AVIV, Israel (AP) — Iran fired a new wave of missile attacks on Israel early Monday, killing at least five people, while Israel claimed in the fourth day of the conflict that it had now achieved “aerial superiority” over Tehran and could fly over the Iranian capital without facing major threats.

The State Department raised its travel advisory for Israel to Level 4, the highest level, amid airstrikes from Iran.

Smoke and missiles have lit up the skies in Israel and Iran in a fierce standoff triggered by fears over Tehran’s expanding nuclear program. Since June 13, hundreds of military strikes have been exchanged as the two nations remain locked in a conflict that shows no signs of abating.

Aerial attacks between Israel and Iran continued overnight into Monday, marking a fourth day of strikes following Israel's Friday attack. That surprise strike hit the heart of Iran's nuclear program, killing several nuclear scientists as well as high-ranking military leaders, according to Israeli officials.

Onlookers gathered on Saturday at a central Tel Aviv residential building next door to Israel’s defense headquarters that was damaged after it took a hit from what appeared to be shrapnel from an overnight missile barrage from Iran.

Israeli citizens were ordered to head to bomb shelters on Friday night amid retaliatory missile strikes from Iran.

Delta Air Lines Inc. and United Airlines Holdings Inc. suspended flights to Tel Aviv following Israel’s bombing of Iran and the closure of Israel’s airspace.