KIEV (AFP) - US Secretary of State John Kerry on Tuesday became the highest-profile foreign diplomat to visit Ukraine's interim government, offering a US$1 billion (S$1.3 billion) support package in the face of an escalating crisis with Russia.

Both the visit and the announcement highlighted Washington's determination to support the authorities in Kiev against Russia as the West grapples with the most serious crisis in the region since the Cold War.

On a grey, foggy day, Kerry looked sombre as he visited Kiev's Shrine of the Fallen, the flower-laden memorial honouring the nearly 100 people killed during last month's Independence Square protests.

Surrounded by a large crowd, he said: "We are going to help you. We are helping you. President Obama is planning for more assistance." He later met leading politicians including former world heavyweight boxing champion Vitaly Klitschko, who is set to run for president in May's election.

During his brief stopover, Kerry was also expected to meet Ukraine's interim president Oleksandr Turchynov and new Prime Minister Arseniy Yatsenyuk.

Russian-backed president Viktor Yanukovych was ousted after the bloodshed in Independence Square, where protesters massed last year to demonstrate against his failure to ratify a trade pact with the European Union.