U.N. Secretary-General Antonio Guterres says he is 'gravely concerned by the latest developments' in the Gaza Strip after Palestinians fired a rocket into Israel, injuring seven people.

Guterres said the rocket attack is 'a serious and unacceptable violation' and urged all sides 'to exercise maximum restraint.' He also noted reports that Israel has responded to the attack, and said 'further escalation is likely to make an already bad situation worse.'

Israeli Prime Minister Benjamin Netanyahu said Monday while visiting the White House that his country has begun responding 'forcefully' to the rocket attack. He said Israel will do 'whatever we must do' to defend itself.

Israel's military said the rocket attack hit a house in central Israel early Monday, in a small town north of Tel Aviv.

The rocket attack was the second launched toward central Israel in recent weeks, and prompted Netanyahu to cut short his trip to Washington.

Hamas' leader, Ismail Haniyeh, said in a statement Monday that his group will respond if Israel retaliates too forcefully to the rocket attack. He said Hamas' militant faction 'will deter the enemy if it exceeds the red lines.'

The attack has raised fears of the possibility of a larger conflict just two weeks before elections in Israel.

VOA's Margaret Besheer contributed to this report.