The State Department says Syria has lodged an official protest with the United States over a reported U.S. helicopter raid Sunday into Syria from Iraq. Officials declined comment about the reported raid, but said cross-border infiltration of militants from Syria remains an issue between the two countries. VOA's David Gollust reports from the State Department.

Officials are acknowledging the Syrian protest, but maintaining silence about the incident itself, in which U.S. helicopters are reported to have attacked a farm house inside Syria near the Iraqi border and killed several people.

At a news briefing, State Department Spokesman Sean McCormack said U.S. charge' d'affaires in Damascus Maura Connelly was summoned to the Syrian Foreign Ministry Sunday to receive a protest.

McCormack said it concerned reports about the activity in the border town, but said any information about what actually occurred would have to come U.S. military sources.

The United States has long expressed concern about border crossings from Syria to Iraq of Islamic militants though in comments Monday McCormack suggested that the problem has diminished of late:

"There has been, over the years, a changed situation. We read a lot about infiltration over the Syrian border, into Iraq, quite a bit three or four years ago - a couple of years ago," he said. "Less so now. That does not mean that there are not continuing issues in that regard."

The United States withdrew its ambassador from Syria in 2005 after the Beirut assassination of former Lebanese Prime Minister Rafik Hariri, in which U.N. investigators implicated Syrian agents.

But the two countries have maintained relations at the charge' level and there has been at least a slight warming of relations in recent months, amid conciliatory moves by Damascus.

Secretary of State Condolezza Rice met briefly on the sidelines of the U.N. General Assembly in September with Syrian Foreign Minister Walid al-Muallem, and Assistant Secretary of State for Near Eastern Affairs David Welch had more lengthy talks with the Syrian official.

McCormack did not discuss the substance of the meetings, but suggested that prospects for better relations with Syria have improved:

"Syria knows what it needs to do in order to play a different role in the region. It has taken some steps in a positive direction," he added. "I would note for example their decision to establish diplomatic relations with Lebanon. That is a positive step. And of course, their decision that they took with the Israelis to have contacts via the Turkish government about coming to a peace settlement."

The United States had long pressed Syria to normalize relations, and demarcate its border with, Lebanon - a country it partially occupied for three decades, until withdrawing under U.N. pressure in 2005.

U.S. financial sanctions against Syria remain in effect over its support for Lebanon's Hezbollah movement and Palestinian radicals opposed to peace efforts with Israel.