French police have detained 300 people after protests in Strasbourg, hours before Barack Obama arrived in France for a two-day Nato summit.
The US President followed French President Nicolas Sarkozy, who touched down this morning ahead of his hosting role at the meeting.
Prime Minister Gordon Brown, buoyed by the confidence in the aftermath of the G20 summit, is also due to arrive shortly.
The Nato summit has already provoked clashes between police and protesters in the French city.
Demonstrators have vowed to disrupt the two-day meeting and police fear violence earlier in the week in London may have encouraged them even more.
Police in Strasbourg used tear gas and rubber bullets to beat back several hundred protesters who threw rocks and bottles at officers yesterday.
Afghanistan is set to dominate the agenda at the summit, which is being held jointly in the French city and Baden-Baden, Germany.