WASHINGTON (Reuters) - The United States pledged US$53 million (S$67 million) in fresh aid to Ukraine on Thursday for its struggle against Russia's incursion, including counter-mortar radar equipment, in a gesture of support for visiting Ukraine President Petro Poroshenko.

Senior Obama administration officials said the new assistance would include US$46 million to bolster Ukraine's security in its conflict with Russian-backed separatists in eastern Ukraine and US$7 million in humanitarian aid.

Announcement of the package came as Mr Poroshenko was in Washington to meet President Barack Obama and make the rounds with lawmakers on Capitol Hill.

The US$46 million in security aid includes for the first time counter-mortar radar detection equipment used to locate incoming artillery fire and increase the ability of Ukrainian security forces to respond.

Other items provided will include engineering equipment, patrol vehicles, personnel transports, small maritime craft, surveillance equipment and some chemical and explosive detection gear, as well as body armour, rations, de-mining equipment and first-aid items, a senior administration official said.

The package does not include the type of lethal weaponry that some Republican lawmakers would like the United States to provide.

A senior administration official said the US assessment is that Ukraine has enough such equipment and that the types of weaponry that has been discussed would be of only marginal value and would not have a decisive effect.

"There's no sense that there's an effective military edge that could be given that could change the overall balance," the official said.

"Ukraine would be extremely vulnerable to a fully supported Russian attack."

The US$7 million in humanitarian assistance is money that will be transferred to international relief organisations to help people in eastern Ukraine.

Commerce Secretary Penny Pritzker will lead a US delegation to Ukraine Sept 26-27 to meet with senior officials and business leaders and discuss Ukraine's economic reform efforts.

The United States and its European allies have imposed several rounds of economic sanctions against Russia for its seizure of Crimea and backing of a separatist movement in eastern Ukraine.