By Barbara Starr, CNN Pentagon Correspondent

(CNN) -- US intelligence is monitoring a series of cargo flights from Iran into Syria that the US suspects may be carrying weapons systems into Syria for potential use by Bashar al-Assad's regime or Iranian forces, CNN has learned.

An administration official confirms to CNN that the flights took place and the US and Israel are both concerned the cargo could potentially include weapons that could eventually be used to threaten Israel.

While weapons shipments into Syria are not uncommon, these flights involving Iran have caught the attention of US intelligence because they occurred in the days after the April 13 US airstrikes on Assad regime targets. Rhetoric between Iran and Israel has also escalated in recent weeks over Tehran's involvement in areas of Syria that can be used to potentially launch missiles or aircraft that could target Israel.

Earlier this week, social media sites that track global air traffic recorded at least two flights by Syrian Air Force IL-76 cargo jets between Iran and Syria. The official said other flights, including at least one from an Iranian cargo jet, have also caught US attention.

Israel reportedly struck several targets inside Syria earlier this month including a T4 airbase in Homs province where Iranians had placed anti-aircraft missiles as well as unmanned aerial vehicles.

Israel has launched attacks on sites in Syria in the past, most notably in February when it struck twelve targets including three aerial defense batteries, as well as four targets which the Israel Defense Forces described as Iranian. That attack came after the shooting down of an Israeli F-16 fighter jet by Syrian forces, and the infiltration of Israeli airspace by what the IDF said was an Iranian drone.

US intelligence assessed the Israeli aircraft may have been shot down by a barrage of anti-aircraft missiles. There are concerns that if the fresh shipments are indeed weapons, they could include more anti-aircraft missiles.

A senior Iranian security official said Iran would punish Israel for the recent airstrikes on the T4 airbase in Homs, according to Iran's semi-official FARS news agency. Ali Shamkhani, the Secretary of Iran's Supreme National Security Council, and former defense minister, said Israel has not yet realized that the era of "hit-and-run" has come to an end and it should pay the price for such "stupidity."

Shamkhani said "When a regime thinks that it is entitled to target counterterrorism troops in a move that comes with a planned violation of another country's airspace, it should have certainly thought of its repercussions and reactions." He added that "There will definitely be a punishment of the aggressor but naturally, the time, place and quality of the response to this vicious act depends on the Islamic Republic's will and choice,"

Russia's Defense Ministry claimed two Israeli F-15 warplanes launched eight guided missiles from Lebanese airspace, targeting the T-4 base in central Syria early this month. The strike resulted in the killing of "some Iranian military advisers,".

Israeli officials have not issued any response to reports of the strikes.