(Adds army details on rocket and mortar firing)

GAZA, Dec 4 (Reuters) - An Israeli air strike killed three Hamas militants and wounded another in the Gaza Strip on Tuesday, Palestinian medical workers and Hamas said.

The missile strike targeted a training base for Hamas's armed wing in southern Gaza, the Islamist group said.

An Israeli army spokeswoman confirmed there had been an air strike on a Hamas military position in Gaza.

Israeli Defence Minister Ehud Barak told ministers this week he had authorised military action in Gaza, including against "manned military Hamas targets".

The Israeli army frequently carries out air strikes against militants in the coastal territory to try to stop them from firing rockets at southern Israeli towns and placing explosives near the border fence targeting Israeli troops.

An Israeli army spokeswoman said Tuesday's firing of some 21 mortars and rockets had taken the total of launchings for 2007 to 2,000.

She added that since Hamas took control of the Gaza Strip in June, the number of rocket and mortar launchings had increased five-fold from about 48 per month to around 240 per month.

Barak said a major ground offensive that Israel has threatened to carry out in the coastal territory which it evacuated in late 2005 was not imminent.

"The time has not come yet, and I hope it will never come, but it is true that we are preparing, and need to prepare, for a wide range of possibilities," Barak told Army Radio.

Israel, which views Gaza as an enemy entity after it was seized by Islamist Hamas in June, has begun cutting fuel supplies to the territory, forcing many filling stations to remain closed on Tuesday. (Reporting by Nidal al-Mughrabi; Writing by Ari Rabinovitch, Editing by Caroline DRees)

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