GAZA, Dec 24 (Reuters) - Gaza's Hamas rulers signalled on Friday they wanted to defuse tension with Israel that has increased over the past week and they reiterated their desire for a mutual ceasefire.

Israel and the Islamist Hamas fought a three-week war in the Gaza Strip two years ago and frequent exchanges of fire have taken place across the tense border since, with incidents rising recently.

Palestinian militants fired 26 rockets and mortars into Israel this week, including one that exploded near a kindergarten. An Israeli air strike wiped out a five-man rocket squad and a Palestinian shepherd was shot dead near the border.

In front of a crowd of supporters in southern Gaza after Friday prayers, senior leader Mahmoud Al-Zahar said Hamas would be committed to a ceasefire if Israel abided by it.

Zahar said Hamas and other factions were committed to an agreement they had reached last year to stop rocket firing into Israel, although smaller groups continued to launch attacks.

Earlier on Friday a rocket and at least one mortar bomb fired from Gaza landed in Israel. The Israelis responded after dark with three air strikes, one of which wounded a Hamas gunman at a training camp in central Gaza, local officials said.

We are committed to self-restraint as long as there is no oppression and no aggression, Zahar said.

Hamas, whose charter calls for the destruction of Israel, has said in the past it could agree to a long-term truce.

A spokesman for Israel's Foreign Ministry said Zahar's declared intentions will be tested by the reality on the ground.

Hamas has escalated the situation, it can now be de-escalated by simply stopping the rocket fire, Yigal Palmor said.

The United Nations said on Thursday both sides had indicated they wanted to reduce tension around the eastern Mediterranean coastal enclave.

Friday's mortar attack on Israel was claimed by Ansar al-Sunna, a small Palestinian faction inspired by al Qaeda and disavowed by Hamas. There was no claim of reponsibility for the rocket launch. Neither incident caused casualties in Israel. (Writing by Nidal al-Mughrabi and Ari Rabinovitch; Editing by Angus MacSwan)