By Patricia Zengerle

WASHINGTON (Reuters) - U.S. Senate leaders said on Tuesday they expect President Joe Biden to send them a request by the end of this week for billions of dollars in assistance for Israel, Ukraine and Taiwan and for security at the U.S. border.

The size of the request was not known, but a congressional source familiar with the request said Israel had asked for $10 billion, as it responds to an attack on its citizens by the Iran-backed militant group Hamas.

Israel's request is not an indication that the Biden administration would request, or Congress would approve, that amount.

"We are going to do everything in our power to ensure the Senate delivers the support for Israel and the rest of the package. We intend to get the package the end of this week," the Senate's majority leader, Democratic Senator Chuck Schumer, told his weekly press conference.

The top Senate Republican, Senator Mitch McConnell, said he expected the request to include assistance for Israel, Ukraine and Taiwan, and said Republicans want it to include "something serious" for the border.

Top Biden administration officials will hold a classified briefing on Wednesday for the Senate on the situation in Israel and Gaza. Schumer said that Democratic Senator Bob Menendez, who faces charges of acting as an unregistered agent for Egypt, would not attend.

Menendez has denied wrongdoing.