Israeli warplanes mounted an attack on a Syrian military base this week, according to an American official cited by US media.
There may be a ceasefire on the surface at the Gaza border, but for the Israeli army the threats can come from underground.
Israel has admitted it fired two missiles in the Mediterranean. It initially denied any knowledge of missiles being fired.
The United States currently has five guided missile destroyers in the eastern Mediterranean Sea - the USS Gravely, the USS Barry, the USS Ramage, the USS Mahan and the USS Stout.
The ships can carry a maximum of 90 to 96 Tomahawk cruise missiles, if loaded only with these weapons. The missiles have a range of around 1,000 miles and it is thought they would be the weapon of choice if President Obama ordered a strike on Syria.
This was the kind of test that Israel carries out every two or three months.
It keeps a variety of missile defence systems in a state of permanent alert and this morning it launched a missile from one of its own aircraft which was flying above the central Mediterranean Sea, in the direction of Israel.
A routine test which took place, of course, at a time and in a place where tensions are very high.
It was the Russians who raised the alarm about a missile launch. They have about a dozen ships from their Mediterranean fleet off the coast of Syria right now. They are keeping a very close eye on what the five American destroyers are doing in the same stretch of sea at the moment.
The US State Department has this morning denied that it was in anyway directly involved in the Israeli test.
So, military action against Syria may not be imminent but we are in a global crisis at the moment, a crisis in which routine tests can become significant.
The US Navy did not fire any missiles from ships in the Mediterranean, a spokesman said.
Israel said it carried out a joint missile test with the US in the Mediterranean, Reuters reported.
A radar in Syria did not detect any missiles landing in the country after the Russian Defence Ministry said it detected two ballistic objects being launched towards the eastern Mediterranean, a security source told Lebanon's Al-Manar TV.
A US official said that no American ships or planes had launched missiles in the Mediterranean, CBS News reported.
Two ballistic objects that the Russian Defence Ministry said it detected being fired towards the eastern coast of the Mediterranean fell into the sea, the state-run Russian news agency RIA cited a source in Damascus as saying.
The Israeli military said it was "not aware" of any missile launches in the eastern Mediterranean after the Russian Defence Ministry said it detected two ballistic objects being fired there.
There is no sign of a missile attack or explosions in Damascus after ballistic launches were detected, the Russian embassy in Syria said.