- Sen. John Kerry said reports that Iran is using Iraqi airspace are troubling
- Kerry says Iran has acknowledged providing training to Syrian forces
- An opposition news agency says one of its journalists has been killed
- Iran's parliament speaker says Tehran has held talks with the opposition
(CNN) -- A U.S. lawmaker warned Iraq to avoid "fanning the flames of violence" by allowing Iran to use its airspace to transport weapons to Syria or face possible sanctions.
The comments by Sen. John Kerry, chairman of the Foreign Relations Committee, on Wednesday follow reports that Iran has been sending weapons through Iraq to Syria, something Iraq has vehemently denied.
Here are the latest key developments in the civil war in Syria:
Stern warning, redux: From the United States
Amid renewed reports that Iraq is failing to inspect shipments from Iran to Syria, Kerry raised the possibility of cutting off aid to Iraq if it didn't take steps to address the issue.
Iraq has repeatedly denied allegations that it has allowed Iran to deliver weapons to Syria. Iran, meanwhile, has denied shipping weapons to President Bashar al-Assad's forces.
Kerry's comments follow a recent visit to Iraq by U.S. Sens. John McCain of Arizona, Joe Lieberman of Connecticut and Lindsey Graham of South Carolina, where the three lawmakers discussed the issue with the prime minister.
The U.S. State Department has said Iran is doing little to hide its support of al-Assad, and it has raised the issue with Iraq. But it stopped short of saying it is convinced that Iran is transporting weapons.
Shiite-dominated Iran is closely allied with Syria's Alawite minority-controlled government. Al-Assad belongs to the Alawite religious group, an offshoot of Shiite Islam.
During a confirmation hearing of the nomination of Robert Beecroft as ambassador to Iraq, Kerry said the issue was an important test case for Iraq.
"It's not surprising that Iraq seeks neighborly relations with Iran. But the reports of Iran using Iraqi airspace to resupply Assad's ruthless regime are troubling," Kerry said.
"Just this week, the commander of the Islamic Revolutionary Guard Corps acknowledged that Iran is providing assistance and training to groups inside Syria, begging the question of how else Iranian materiel might get into Syria. This is a problem, and it will only grow worse if not addressed."
During the hearing, Kerry said Iraq could not have it both ways -- receiving aid from the United States and allowing Iran to transport weapons that are used to kill people in Syria.
Carnage continues: Report of burned bodies
A reporter for the opposition's Shaam News Network was among four men who were killed and their bodies burned in Hama when regime forces set fire to a house, the news agency claimed late Wednesday.
Adbelkareen Al'uqda, 26, used the monikers Abu Hassan and Karmo, in reports, the news network said. He is credited with uploading more than 1,250 videos on YouTube that captured the violence between government forces and rebels, it said.
The network said Al'uqda was with three friends at a home preparing for a day of filming when al-Assad's forces ambushed them, shooting them and then setting the house on fire.
CNN cannot independently confirm reports of violence as the Syrian government has severely limited the access of international journalists.
At least six people were killed in fighting early Thursday, with four of the casualties in the flashpoint city of Aleppo -- Syria's largest city, according to the Local Coordination Committees of Syria, an opposition group.
The report of the killings comes amid reports by human rights agencies that say there is evidence that both sides have committed war crimes, though the majority of the allegations are against al-Assad's forces.
More than 26,000 people have been killed since the uprising began in March 2011, the LCC said.
Iranian diplomacy: Meeting the opposition
Iran's Parliament Speaker Ali Larijani revealed that his country has held talks with Syrian opposition groups, according to a transcript of an interview released by the Financial Times.
In the interview, Larijani said according to reports he received there was contact with the Muslim Brotherhood of Syria "to bring about peace and to support necessary reforms."
It was unclear when the discussions were held or whether they yielded any progress, though Larijani said the were held in Tehran.
Larijani described the Syrian opposition as "multilayered," without a unified leader.
"The have various intentions and opinions," he told the newspaper.
Report: Turkish aircraft was over international waters
A Turkish military prosecutor says forensic evidence shows that the June 22 downing of their jet by a surface-to-air missile fired by Syria occurred over international waters, the semi-official news agency Anadolu Agency reported.
Syria shot down the F-4 Turkish Phantom jet on June 22, intensifying the animosity between the countries, whose once-close relationship has eroded since al-Assad's forces began cracking down on opposition last year.
Syria claimed the plane violated its airspace, an allegation that Turkey vehemently disputed.
CNN's Hamdi Alkhshali and Amir Ahmed contributed to this report.