CAIRO/GAZA, Dec 20 (Reuters) - Israeli troops and Hamas militants fought fierce gunbattles on the streets of Gaza's second-biggest city on Wednesday as the United Nations delayed a vote on a bid to boost aid deliveries to the Palestinian enclave facing a humanitarian disaster.

Israel's campaign to eradicate Hamas militants behind an Oct. 7 massacre has left the coastal enclave in ruins, brought widespread hunger and homelessness, and killed nearly 20,000 Gazans, according to the Palestinian enclave's health ministry.

Under foreign pressure to avoid killing innocents, Israeli Prime Minister Benjamin Netanyahu says the war will not stop until Iran-backed Hamas releases the remaining 129 hostages it is holding in Gaza and the Islamist group is obliterated.

A United Nations Security Council vote to set up aid deliveries was delayed by another day on Tuesday as talks continue to try and avoid a third U.S. veto of action over the two-month long Israel-Hamas war.

The 15-member council was initially going to vote on a resolution - drafted by the United Arab Emirates - on Monday. But it has repeatedly been delayed as diplomats say the UAE and the U.S. struggle to agree language citing a cessation of hostilities and a proposal to set up U.N. aid monitoring.

When asked if they were getting close to an agreement, U.S. Ambassador to the U.N. Linda Thomas-Greenfield told reporters on Tuesday: "We're trying, we really are."

The conflict has spread beyond Gaza, including into the Red Sea where Iran-aligned Houthi forces based in Yemen have been attacking commercial vessels with missiles and drones, prompting the creation of a multinational naval operation to protect trade routes.

U.S. Defense Secretary Lloyd Austin said in Bahrain that joint naval patrols would be held in the southern Red Sea and Gulf of Aden, which encompass a major East-West global shipping route.

"This is an international challenge that demands collective action," Austin said.

British maritime security firm Ambrey said on Tuesday it received information of an unsuccessful boarding attempt west of Yemen's Aden port city.

Some shippers are re-routing around Africa.

The Houthis said they would carry on attacking commercial shipping in the vital trade route, possibly with a sea operation every 12 hours.

"Our position in support of Palestine and the Gaza Strip will remain until the end of the siege, the entry of food and medicine, and our support for the oppressed Palestinian people will remain continuous," Houthi official Mohammed Abdulsalam told Reuters, saying only Israeli ships or those going to Israel would be targeted.

Photo from Reuters