Hundreds of demonstrators have rioted outside the US embassy in Mexico City, in the latest protest against President George W Bush's tour of Latin America.
Many people were protesting against the war in Iraq
Protesters burned US flags and threw stones at police guarding the building.
Tear gas was used to disperse the crowds. Several people were injured, including a number of police officers.
The violence came hours after Mr Bush pledged to reform controversial immigration laws, during two-day talks with Mexican President Felipe Calderon.
Mr Bush made the announcement on Tuesday at the start of talks with Mr Calderon. The two leaders are also expected to tackle the issue of drug trafficking.
There have been protests at each stage of Mr Bush's trip, and verbal attacks on him by Venezuela's Hugo Chavez, who is on his own tour of the region.
The US president has visited Brazil, Uruguay, Colombia and Guatemala. Mexico is the final stop on his seven-day tour of the region.
The leaders' summit is being held in the eastern city of Merida. Correspondents say that without a president nearby, the rioters in Mexico City turned their anger against the US embassy.
Reports say hundreds of people were involved - most were protesting against the war in Iraq rather than President Bush's policies on Latin America.
There have been some small-scale protests in Merida.
Earlier, President Bush promised to work hard to achieve a more sensitive and "comprehensive" immigration policy involving Mexicans.
The US is planning to construct hundreds of kilometres of fencing along the border to try to prevent the flow of illegal immigration from Mexico - something Mr Calderon has strongly criticised.
Mr Calderon repeated his criticisms of the plans on Tuesday, saying that migration could not be stopped by building a fence.
President Bush is unlikely to offer more concessions other than his already stated desire for a guest-worker programme for Mexicans living illegally in the US.
The BBC's Duncan Kennedy in Merida says that after a week travelling through five countries Mr Bush's visit is being judged to be more of a symbolic success than one involving new policies or additional aid.
But with his agenda crowded by the events in the Middle East, the president will probably be satisfied with that, our correspondent says.
Venezuelan President Hugo Chavez has used a parallel trip to speak out against what he calls the interference of the "American empire".
Mr Chavez' last stop was Haiti where he signed a deal granting the island 14,000 barrels of crude a day as a beneficiary of Venezuela's PetroCaribe initiative, which offers regional governments discounted oil supplies.
In a joint press conference, Haitian President Rene Preval also said his country had signed a three-way deal with close allies Venezuela and Cuba on health care, energy and oil.
Mr Chavez began his tour in Argentina last week, where he was the main speaker at a huge anti-Bush rally, and has also visited Bolivia and Nicaragua and Jamaica.