George W. Bush landed at Boryspil airport near Kiev a few hours after Secretary of State Condoleezza Rice. The visit is a stop-over before the April 2-4 NATO summit in Romania, which Russian President Vladimir Putin will also be attending, as a guest.
More than 5,000 police have been deployed in Ukraine's capital, Kiev, in advance of Bush's meeting with President Viktor Yushchenko.
The presidents will hold closed-door talks at 9:00 a.m. local time (07:00 GMT) at the presidential office near the city's main square, where protesters have pledged to continue yesterday's mass rally against Bush's visit and the Ukrainian leadership's plans to join NATO.
Bush will also meet with Ukrainian Prime Minister Yulia Tymshenko, a key figure in the 2004 "orange revolution" that brought Yushchenko to power, parliamentary speaker Arseniy Yatsenyuk, and the main opposition leader, Kremlin-friendly former premier Viktor Yanukovych.
Ukraine's leaders requested in January to join NATO's Membership Action Plan (MAP), a program that prepares countries for accession to the Western military alliance but does not guarantee membership.
However, despite Washington's unequivocal support for Ukraine's bid, membership is far from certain, with the majority of Ukrainians and a vocal minority in parliament resisting the plans, partly over fears of provoking former Soviet master Russia. The Kremlin threatened in February to target missiles at Ukraine if Kiev joins NATO and allows Western military facilities on its territory.
Bush, now in his last year in power and with his popularity at an all-time low five years on from the Iraq invasion, will try to encourage NATO members in Bucharest to bring Ukraine and ex-Soviet Georgia into MAP, but is likely to face resistance from France and Germany.
While in Kiev, Bush and his wife Laura will accompany Viktor and Katerina Yushchenko to a flower-laying ceremony at the memorial to Ukraine's 1932-1933 famine, known as Holodomor. Kiev considers the famine an act of genocide against Ukrainians by the Soviet Union.
On Monday, thousands of people gathered on Kiev's Independence Square (Maidan Nezalezhnosti) to rally against Bush and NATO, displaying banners with the slogans "NATO is worse than the Gestapo" and "Put Bush's bloody dictatorship under an international tribunal."
A protest organizer said between eight and nine thousand people are expected to take part in today's protest, which will run until April 4, the final day of the NATO summit.
Ukraine's drive toward NATO membership has triggered domestic parliamentary opposition protests amid widespread antipathy toward the alliance. A survey published earlier this month said only 11% of Ukrainians supported the idea of NATO membership, while almost 36% were strongly opposed.
